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NorthWestern’s current 3 electric service charges are below cost-based levels. 4 5 Table 1 6 Comparison of Current and Cost-Based Service Charges - Electric Current Rate 07/01/2024 Cost- Based Rate Current / Cost- Based (%) ∆ Current to Cost- Based ($) ∆ Current to Cost- Based (%) Residential (Monthly) Service Charge $4.20 $13.77 30.5% $9.57 227.8% GS-1 Secondary (Monthly) Non-Demand $6.00 $22.11 27.1% $16.11 268.5% Demand $8.70 $32.06 27.1% $23.36 268.5% GS-1 Primary (Monthly) Non-Demand $8.80 $235.29 3.7% $226.49 2573.7% Demand $27.70 $740.62 3.7% $712.92 2573.7% GS-2 Substation (Monthly) Service Charge $286.45 $1,780.28 16.1% $1,493.83 521.5% GS-2 Transmission (Monthly) Service Charge $1,380.00 $1,831.14 75.4% $451.14 32.7% Irrigation (Annual) Non-Demand $45.20 $236.59 19.1% $191.39 423.4% Demand $106.50 $557.45 19.1% $450.95 423.4% 7 NorthWestern’s proposed changes to electric monthly service charges are 8 presented below in Table 2., Please describe NorthWestern’s proposal to increase demand charges 2 for electric service customers. 3 A., Fang, NorthWestern proposes to increase the existing 4 demand charges for non-residential customers to be more cost-based. 5 6 Currently, NorthWestern’s electric monthly demand charges are below cost- 7 based levels., Please describe NorthWestern’s proposal to increase monthly demand 3 charges for natural gas service customers. 4 A., NorthWestern proposes to adjust its Natural Gas monthly demand charges to 5 be more cost-based.

CUSTOMER LOAD GROWTH AND DEMAND-SIDE MANAGEMENT _____ a., DEMAND-SIDE MANAGEMENT 43 7., As natural gas demand continues to grow, additional supply and transmission infrastructure will need to be developed to address future increases in demand., NorthWestern’s Energy Supply function is then charged with ensuring it has enough natural gas supply lined up to meet Design Day needs., Storage is filled in the summer during months of low demand.

RATE Customer charge per month – negotiated rate not to exceed* $330.00 Demand Charge – Extended Service: (Firm Supply Only) Pertherm daily contract demand 1 s t 5 0 0 t h e r m s / d a y (never less than 50 therms) $0.24590 O v e r 5 0 0 t h e rms/day $ 0 .00000 Non-Gas Transportation Rate (Rate 94)* Negotiated R a t e P e r T h e rm Not to Exceed ......... $0.05911 CityApproved Economic Development Surcharge $ 0 .00254 (Includes Kearney, North Platte and Grand Island., Minimum Charge Customer Charge + Demand Charge(if applicable) *In no event shall the demand charge (if applicable), plus the total of the customer charge and the revenue from the transportation rate, be less than the incremental cost of serving each customer in this class., T h e c u s t o m e r s h a l l b e r e s p o n s i b l e f o r any imbalance or other charges or penalties in the event such charges are levied against the Company by pipeline transporters in connection with loads transported pursuant to this tariff schedule. 4., I f t h e c u s t omer takes unauthorized gas during the periods of curtailment, a penalty rate which is the greater of $3.00 per therm or the maximum penalty charges permitted to be made by the Company’s upstream service providers for takes of natural gas in addition to the regular Commodity Charge for such gas.

Minimum C h a r g e Theminimum monthly bill will be the demand charge for 5 kilowatt plus actual energy charges., Maximum Charge Themaximum monthly charge shall be the higher of (1) the minimum charge or (2) the combined average cost of $0.25 per kilowatt hour for demand and energy charges., Energy C h arge Perkilowatt hour for the first 100 hours of the maximum demand (never less than 100 kilowatts) . . . . . . . . . . . . . . . . $ 0 . 0 6 2 7 9 Perkilowatt hour for the next 300 hours of the maximum demand (never less than 100 kilowatts) . . . . . . . . . . . . . . . . $ 0 . 0 3 0 0 1 Perkilowatt hour for the next 100 hours of the maximum demand (never less than 100 kilowatts) . . . . . . . . . . . . . . . . $ 0 . 0 2 0 3 8 Perkilowatt hour for all use in excess of 500 hoursuseof the maximum demand (never less than 1 0 0 k i l o w a t ts) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 0 . 0 1 0 7 5 Minimum C h a r g e Theminimum monthly bill will be the demand charge plus the energy charge of 100 hours use thereof., The rate for this service will be $3.24 per Kw of demand., The monthly standby demand charge will be based on the trailing 12 month peak demand at the time of execution of the contract.

In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h).

Max Kilowatts Delivered 04 = Max Kilowatts Delivered The current max demand is displayed in kilowatts., Demand charges are for customers with a demand rate type., This screen is displayed whether they are a demand customer or not.

In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h).

 NorthWestern Energy Schedule O‐8 Electric Utility ‐ State of South Dakota Page 1 of 2 Pro Forma Year Ending December 31, 2022 Derivation of Increased Rates and Proof of Revenue Billing Billing Line Description Units Rate Revenue Units Rate Revenue $ % 1 Commercial & Industrial Service Rate 33 2 Summer Rate 3 Demand Charge 237,921 $11.05 $2,629,024 237,921 $14.13 $3,361,819 $732,796 27.87% 4 Power Factor Charge 294,039 $14.13 375,997 81,958 27.87% 5 First 100 kWh per kW 21,584,573 $0.06659 1,437,317 21,584,573 $0.07887 1,702,375 265,059 18.44% 6 Next 300 kWh per kW 33,383,062 $0.04580 1,528,944 33,383,062 $0.05424 1,810,697 281,753 18.43% 7 Next 100 kWh per kW 1,862,545 $0.02706 50,400 1,862,545 $0.03204 59,676 9,275 18.40% 8 Over 500 kWh per kW 642,889 $0.01455 9,354 642,889 $0.01723 11,077 1,723 18.42% 9 Primary Discount 10 MAX33 Revenue ‐343,438 ‐406,686 ‐63,248 18.42% 11 Sub‐total Summer Rate 57,473,069 $5,605,640 57,473,069 $6,914,956 $1,309,316 23.36% 12 Booked, to Billed Revenue Ratio 100.041% 100.00% 13 Booked Base Rate Revenue $5,607,952 $6,914,956 $1,307,004 23.31% 14 Off‐Peak Rate 15 Demand Charge 440,506 $11.05 $4,867,594 440,506 $14.13 $6,224,354 $1,356,759 27.87% 16 Power Factor Charge 429,319 548,984 119,665 27.87% 17 First 100 kWh per kW 39,856,971 $0.06659 2,654,076 39,856,971 $0.07887 3,143,519 489,444 18.44% 18 Next 300 kWh per kW 59,102,384 $0.04580 2,706,889 59,102,384 $0.05424 3,205,713 498,824 18.43% 19 Next 100 kWh per kW 3,073,121 $0.02706 83,159 3,073,121 $0.03204 98,463 15,304 18.40% 20 Over 500 kWh per kW 1,276,166 $0.01455 18,568 1,276,166 $0.01723 21,988 3,420 18.42% 21 Primary Discount 22 MAX33 Revenue ‐661,833 ‐783,716 ‐121,883 18.42% 23 Sub‐total Off‐Peak Rate 103,308,642 $10,097,772 103,308,642 $12,459,306 $2,361,534 23.39% 24 Booked to Billed Revenue Ratio 99.894% 100.00% 25 Booked Base Rate Revenue $10,087,099 $12,459,306 $2,372,207 23.52% 26 27 Annual Subtotal Rate 33 160,781,711 $15,703,412 160,781,711, $19,374,262 3,670,850 23.38% 28 Booked to Billed Revenue Ratio 99.947% 100.000% 29 Total Adjusted Annual Commercial Rate 33 Revenue 160,781,711 $15,695,051 160,781,711 $19,374,262 3,679,211 23.44% ‐‐‐‐‐‐‐‐‐‐ Present Rates ‐‐‐‐‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐‐‐‐ Proposed Rates ‐‐‐‐‐‐‐‐‐‐ Revenue Change NorthWestern Energy Schedule O‐8 Electric Utility ‐ State of South Dakota Page 2 of 2 Pro Forma Year Ending December 31, 2022 Derivation of Increased Rates and Proof of Revenue Billing Billing Line Description Units Rate Revenue Units Rate Revenue $ % 1 Commercial & Industrial Service Rate 33YS 2 Summer Rate 3 Demand Charge 1,006 $11.05 $11,122 1,006 $14.13 $14,222 $3,100 27.87% 4 Power Factor Charge 0 0 0 0.00% 5 First 100 kWh per kW 100,518 $0.06659 6,693 100,518 $0.07887 7,928 1,234 18.44% 6 Next 300 kWh per kW 153,844 $0.04580 7,046 153,844 $0.05424 8,344 1,298 18.43% 7 Next 100 kWh per kW 0 $0.02706 0 0 $0.03204 0 0 #DIV/0!, 8 Over 500 kWh per kW 0 $0.01455 0 0 $0.01723 0 0 0.00% 9 MAX33 Revenue 0 0 0 $0.00000 0 0 0.00% 10 YS Discount 4,252 0 $0.00000 4,252 0 0.00% 11 Sub‐total Summer Rate Before YS Discount 254,362 $24,861 254,362 $30,494 5,633 22.66% 12 Booked to Billed Revenue Ratio 100.167% 100.00% 13 Booked Base Rate Revenue $24,903 $30,494 5,591 22.45% 14 Off‐Peak Rate 15 Demand Charge 1,432.75 $11.05 $15,832 1,433 $14.13 $20,245 $4,413 27.87% 16 Power Factor Charge 187 239 52 27.87% 17 First 100 kWh per kW 143,317 $0.06659 9,543 143,317 $0.07887 11,303 1,760 18.44% 18 Next 300 kWh per kW 239,507 $0.04580 10,969 239,507 $0.05424 12,991 2,021 18.43% 19 Next 100 kWh per kW 0 $0.02706 0 0 $0.03204 0 0 0.00% 20 Over 500 kWh per kW 0 $0.01455 0 0 $0.01723 0 0 0.00% 21 MAX33 Revenue 0 0 $0.00000 0 0 0.00% 22 YS Discount 6,400 0 $0.00000 6,400 0 0.00% 23 Sub‐total Off‐Peak Rate Before YS Discount 382,824 $36,532 382,824 $44,778 $8,246 22.57% 24 Booked to Billed Revenue Ratio 99.538% 100.00%

RAT E S N AT U R A L GAS RAT E S Customers are billed for supply, transmission, distribution, storage, Universal Systems Benefts, competitive transmission charges, a distribution charge, and delivery/supply taxes., RAT E S RESIDENTIAL CUSTOMER JUNE 2023 MONTHLY NATURAL GAS BILL COMPONENTS USING 100 THERMS PER MONTH COMMERCIAL CUSTOMER JUNE 2023 MONTHLY NATURAL GAS BILL COMPONENTS USING 200 THERMS PER MONTH Supply & Deferred Supply 29% Delivery & Storage Charges 40% Service Charge 12% Taxes 18% Supply & Deferred Supply 30% Delivery & Storage Charges 40% Service Charge 9% Taxes 21% NORTHWESTERN ENERGY’S JUNE 1, 2023 ELECTRIC COSTS BY SIZE & CUSTOMER TYPE 1 Residential Commercial Industrial GS1 Secondary Non Demand GS1 Secondary Demand GS1 Primary Demand GS2 Substation Demand Monthly kWh 750 1,500 14,000 180,000 650,000 Peak Monthly kW Demand N/A N/A 40 500 1,000 TOTAL ELECTRIC COSTS (supply, distribution, transmission & other charges) Monthly Cost $109.60 $236 $1,856 $21,758 $60,029 Average Cost per kWh for Supply and Delivery $0.1461 $0.1573 $0.1326 $0.1209 $0.0924 NORTHWESTERN SUPPLY R E L ATED COSTS 2 Supply Portion of Monthly Bill $58 $118 $1,100, ELECTRIC SERVICE CONSTRUCTION CHARGES Upon application for electric service, the Utility shall make an extension of the primary and/or secondary line free of charge to the applicant up to the level of the costs shown below, but no greater than the entire actual cost of such line extension as defned in Montana Public Service Commission Electric Ta r i f, Rule 6-1., • Demand General Service Commercial and Irrigation Metered Services equal to or greater than 1 MW Allowance; calculated based on a Revenue/Cost Ratio., NAT U R A L GAS SERVICE CONSTRUCTION CHARGES Upon application for natural gas core service, the Utility shall make an extension of the distribution main pipeline free of charge to the applicant for service up to the level of the costs shown below, but no greater than the entire actual cost of such line extension: • Residential Customer - $890 allowance toward construction costs

 NorthWestern Energy Schedule O‐9 Electric Utility ‐ State of South Dakota Page 1 of 5 Pro Forma Year Ending December 31, 2022 Derivation of Increased Rates and Proof of Revenue Billing Billing Line Description Units Rate Revenue Units Rate Revenue $ % 1 Large Commercial and Industrial Rate 34 2 Summer Rate 3 Demand Charge ‐ First 100 kW 203,100 $11.05 $2,244,259 203,100 $14.13 $2,869,808 $625,549 27.87% 4 Demand Charge ‐ Next 400 kW 198,557 $9.79 1,943,877 198,557 $12.52 2,485,938 542,062 27.89% 5 Demand Charge ‐ Next 500 kW 186,424 $8.53 1,590,199 186,424 $10.91 2,033,888 443,690 27.90% 6 Total Demand Charge 588,082 $5,778,334 588,082 $7,389,634 $1,611,300 27.89% 7 Power Factor Charge Revenue 168,515 215,486 46,971 27.87% 8 MIN34 Revenue 42,971 54,940 11,969 27.85% 9 Energy Charge ‐ First 100 X Demand 58,097,495 $0.04911 2,853,168 58,097,495 $0.06279 3,647,942 794,774 27.86% 10 Energy Charge ‐ Next 300 X Demand 141,880,980 $0.02348 3,331,365 141,880,980 $0.03001 4,257,848, 55,572 12,107 27.86% 10 Energy Charge ‐ Next 300 X Demand 2,653,500 $0.02348 62,304 2,653,500 $0.03001 79,632 17,327 27.81% 11 Energy Charge ‐ Next 100 X Demand 686,700 $0.01595 10,953 686,700 $0.02038 13,995 3,042 27.77% 12 Energy Charge ‐ Remaining kWh 72,500 $0.00841 610 72,500 $0.01075 779 170 27.82% 13 Total Energy Charge 4,297,750 $117,332 4,297,750 $149,978 $32,647 27.82% 14 Sub‐total Summer Rate $201,920 $258,157 $56,237 27.85% 15 Booked to Billed Revenue Ratio 100.181% 100.00% 16 Booked Base Rate Revenue $202,285 $258,157 $55,872 27.62% 17 Off‐Peak Rate 18 Demand Charge ‐ First 100 kW 1,600 $11.05 $17,680 1,600 $14.13 $22,608 $4,928 27.87% 19 Demand Charge ‐ Next 400 kW 5,790 $9.79 56,687 5,790 $12.52 72,494 15,807 27.89% 20 Demand Charge ‐ Next 500 kW 3,526 $8.53 30,076 3,526 $10.91 38,468 8,392 27.90% 21 Total Demand Charge 10,916 $104,443 10,916 $133,570 $29,127 27.89% 22 Power Factor Charge Revenue 223 285 62 28.07% 23 Option L Discount ‐2,780 ‐3,554 ‐774 27.84%, 10 Energy Charge ‐ Next 300 X Demand 8,284,458 $0.02348 194,519 8,284,458 $0.03001 248,617 54,098 27.81% 11 Energy Charge ‐ Next 100 X Demand 1,335,191 $0.01595 21,296 1,335,191 $0.02038 27,211 5,915 27.77% 12 Energy Charge ‐ Remaining kWh 1,026,144 $0.00841 8,630 1,026,144 $0.01075 11,031 2,401 27.82% 13 Total Energy Charge 13,527,522 $365,967 13,527,522 $467,803 $101,836 27.83% 14 Sub‐total Summer Rate $621,770 794,973 173,203 27.86% 15 Booked to Billed Revenue Ratio 100.191% 100.00% 16 Booked Base Rate Revenue $622,957 $794,973 $172,015 27.61% 17 Off‐Peak Rate 18 Demand Charge ‐ First 100 kW 1,900 $11.05 $20,995 1,900 $14.13 $26,847 $5,852 27.87% 19 Demand Charge ‐ Next 400 kW 7,144 $9.79 69,940 7,144 $12.52 89,443 19,503 27.89% 20 Demand Charge ‐ Next 500 kW 51,120 $8.53 436,055 51,120 $10.91 557,721 121,666 27.90% 21 Total Demand Charge 60,164 $526,990 60,164 $674,011 $147,021 27.90% 22 Power Factor Charge Revenue 45,842 58,620 12,778 27.87% 23 Option L Discount $0.00000, 27.86% 10 Energy Charge ‐ Next 300 X Demand 10,656,818 $0.02348 250,222 10,656,818 $0.03001 319,811 69,589 27.81% 11 Energy Charge ‐ Next 100 X Demand 3,262,531 $0.01595 52,037 3,262,531 $0.02038 66,490 14,453 27.77% 12 Energy Charge ‐ Remaining kWh 2,342,660 $0.00841 19,702 2,342,660 $0.01075 25,184 5,482 27.82% 13 Total Energy Charge 19,894,065 $500,331 19,894,065 $639,542 $139,210 27.82% 14 Sub‐total Summer Rate $838,795 1,072,431 233,636 27.85% 15 Booked to Billed Revenue Ratio 100.178% 100.00% 16 Booked Base Rate Revenue $840,292 $1,072,431 $232,139 27.63% 17 Off‐Peak Rate 18 Demand Charge ‐ First 100 kW 2,000 $11.05 $22,100 2,000 $14.13 $28,260 $6,160 27.87% 19 Demand Charge ‐ Next 400 kW 7,191 $9.79 70,402 7,191 $12.52 90,034 19,632 27.89% 20 Demand Charge ‐ Next 500 kW 43,206 $8.53 368,550 43,206 $10.91 471,381 102,831 27.90% 21 Total Demand Charge 52,398 $461,052 52,398 $589,675 $128,623 27.90% 22 Power Factor Charge Revenue 56,262 71,944 15,682 27.87% 23 Option, 8,237 1,792 27.81% 11 Energy Charge ‐ Next 100 X Demand 7,157 $0.01595 114 7,157 $0.02038 146 32 27.77% 12 Energy Charge ‐ Remaining kWh 0 $0.00841 0 0 $0.01075 0 0 0.00% 13 Total Energy Charge 381,755 $11,476 381,755 $14,669 $3,194 27.83% 14 Sub‐total Summer Revenue Before YS Discount 22,286 28,493 6,207 27.85% 15 Booked to Billed Revenue Ratio 100.174% 100.00% 16 Booked Base Rate Revenue $22,324 $28,493 $6,168 27.63% 17 Off‐Peak Rate 18 Demand Charge ‐ First 100 kW 1,600 $11.05 $17,680 1,600 $14.13 $22,608 $4,928 27.87% 19 Demand Charge ‐ Next 400 kW 263 $9.79 2,579 263 $12.52 3,299 719 27.89% 20 Demand Charge ‐ Next 500 kW 0 $8.53 0 0 $10.91 0 0 0.00% 21 Total Demand Charge 1,863 $20,259 1,863 $25,907 $5,647 27.87% 22 Power Factor Charge Revenue 1 1 $0 81.82% 23 YS Discount $0.00000 ‐11,389 0 $0.00000 ‐11,389 24 Energy Charge ‐ First 100 X Demand 186,348 $0.04911 $9,152 186,348 $0.06279 11,701 $2,549 27.86% 25 Energy Charge ‐ Next 300 X Demand 473,474 $0.02348 11,117

Environmental Protection Agency (EPA) -AFederal agency charged with protecting the environment., The demand for natural gas largely depends upon weather conditions., Thus, the rates we are allowed to charge may or may not match our costs at any given time., Demand for our Montana transmission capacity fluctuates with regional demand, fuel prices and weather related conditions., This charge is recorded within other income, net on the Consolidated Statements of Income.

In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h).

SOUTH DAKOTA GAS RATE SCHEDULE | Contract Sales Service | Rate No. 86

SOUTH DAKOTA ELECTRIC RATE SCHEDULE | NORTHWESTERN ENERGY PUBLIC SERVICE CORPORATION d/b/a NORTHWESTERN ENERGY

In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h).

. . . . . . . . . . $ 0 . 0 1 4 5 5 0 .01723 Minimum C h a r g e Theminimum monthly bill will be the demand charge for 5 kilowatt plus actual energy charges., Maximum Charge Themaximum monthly charge shall be the higher of (1) the minimum charge or (2) the combined average cost of $0.20 0.25 per kilowatt hour for demand and energy charges., Energy C h arge Perkilowatt hour for the first 100 hours of the maximum demand (never less than 100 kilowatts) . . . . . . . . . . . . . . . . $ 0 . 0 4 9 1 1 0 .06279 Perkilowatt hour for the next 300 hours of the maximum demand (never less than 100 kilowatts) . . . . . . . . . . . . . . . . $ 0 . 0 2 3 4 8 0 .03001 Perkilowatt hour for the next 100 hours of the maximum demand (never less than 100 kilowatts) . . . . . . . . . . . . . . . . $ 0 . 0 1 5 9 5 0 .02038 Perkilowatt hour for all use in excess of 500 hoursuseof the maximum demand (never less than 1 0 0 k i l o w a t ts) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 0 . 0 0 8 4 1 0 .01075 Minimum C h a r g e Theminimum monthly bill will be the demand charge plus the energy charge of 100 hours use thereof., The rate for this service will be $3.24 per Kw of demand., The monthly standby demand charge will be based on the trailing 12 month peak demand at the time of execution of the contract.

In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (k), provide revenues from demand charges related to the billing demand reported in column (h).

The supply portion of the bill for natural gas is subject to twice yearly fuel cost adjustments and is shown separately from the delivery charge., ELECTRIC RAT E S Components displayed on the bill include: energy, demand, fuel and power factor., The chart to the right shows these various billing components for a NorthWestern Energy commercial customer with a monthly usage of 14,000 kWh and 40 kW demand., RAT E S NORTHWESTERN ENERGY’S JUNE 1, 2023 ELECTRIC COSTS BY SIZE & CUSTOMER TYPE 1 Residential Commercial Industrial GS1 Secondary Non Demand GS1 Secondary Demand GS1 Primary Demand GS2 Substation Demand Monthly kWh 750 1,500 14,000 180,000 650,000 Peak Monthly kW Demand N/A N/A 40 500 1,000 TOTAL ELECTRIC COSTS (supply, distribution, transmission & other charges) Monthly Cost $109.60 $236 $1,856 $21,758 $60,029 Average Cost per kWh for Supply and Delivery $0.1461 $0.1573 $0.1326 $0.1209 $0.0924 NORTHWESTERN SUPPLY R E L ATED COSTS 2 Supply Portion of Monthly Bill $105 $229 $1,299 $16,703 $61,251 Supply Cost as % of To t a l 9 6 % 9 7 % 7 0 % 7 7 % 1 0 2 % S u p p l y C o s t p e r kWh $0.1405 $0.1530 $0.0928 $0.0928 $0.0942 1 Actual Monthly Rates efective June 2023. 2 Supply Costs are subject to periodic adjustments and include supply, deferred supply and supply taxes., SOUTH DAKOTA NORTHWESTERN ENERGY COMMERCIAL CUSTOMER MONTHLY NATURAL GAS BILLING COMPONENTS JULY 1, 2023 USING 200 THERMS PER MONTH NEBRASKA NORTHWESTERN ENERGY COMMERCIAL CUSTOMER MONTHLY NATURAL GAS BILLING COMPONENTS JULY 1, 2023 USING 200 THERMS PER MONTH Monthly Service Charge 6% Monthly Service Charge 5% Delivery Charge (with 2% MGP Refund Included) 19% Delivery Charge 16% Purchased Gas Commodity 75% Purchased Gas Commodity 79% ECONOMIC CONTRIBUTION NorthWestern Energy spent about $562 million in capital across its service territory in 2023.

Demand reported in column (h) must be in megawatts., In column (k), provide revenues from demand charges related to the billing demand reported in column (h)., In column (I), provide revenues from energy charges related to the amount of energy transferred., In column (e) report the demand charges and in column (f) energy charges related to the amount of energy transferred., Report in column (h) the total charge shown on bills rendered to the respondent.

Monthly Charges: Option A Option B Customer Charge p e r Meter: $ 1 2 0 . 0 0 $ 3 2 0 . 0 0 N o n - G a s C o m m odity Charge, all use, per therm: $0.0832 $0.0438 DemandCharge per therm of daily firm demand as shown on Sheet 9a., Gas Demand Payment Elections A., Seasonally p r ofiled January & February 20% of annual charge per month March & December 15%ofannual charge per month April & November 10%ofannual charge per month May & October 5% of annual charge per month June through September 0%of annual charge per month C., Minimum Monthly Bill: The Customer Charge plus the amount for therms of firm demand (never less than 50 therms)., (Sheet Nos. 12, 12a) 4.Penalty P r ovision If customer fails to comply with Company’s request to curtail or in any way fails to limit the use of gas to the volume of Daily Demand , then all unauthorized gas in excess of Daily Demand so used shall be “Penalty Gas” and be paid by the Customer at a rate which is the greater of $3.00 per therm or the maximum penalty charges permitted to be made by the Company’s upstream service providers for takes of natural gas in excess of authorized limitations, in addition to the regular Commodity Charge for such gas.