Time-of-use break-even calculator

Find the peak share that changes the answer

This calculator compares a flat energy rate with a two-period time-of-use energy rate. Supply and delivery must be on the same basis: either include the variable delivery rate in all three rates or exclude it from all three. Enter the monthly fixed fee for each option separately. Defaults are illustrative.

Time-of-use cost equals kWh × [peak share × peak cents + (1 − peak share) × off-peak cents] ÷ 100 + fixed fee. Flat cost equals kWh × flat cents ÷ 100 + fixed fee. For 800 kWh, a 16-cent flat rate costs $128 before fees. A 30-cent peak and 10-cent off-peak plan at a 30% peak share also costs $128. A $12 fee on each plan leaves a tie at $140.

Change peak share to 20% and the time-of-use total falls to $124 with the same fee. This does not mean you can actually shift that much load. Use interval data aligned to the utility tariff, including weekends, holidays, seasons, and daylight saving rules. The tool supports only two periods; use a spreadsheet for additional bands. Zero usage makes a peak-share threshold inapplicable. If peak and off-peak rates are equal, the difference is independent of peak share.