Time-of-use electricity cost calculator

A single average rate can hide the cost of running an appliance during expensive hours. Enter energy used in each rate window to compare the same total consumption fairly.

Enter your own tariff and energy use

The starting numbers below are an invented monthly example, not a utility tariff. Enter dollars per kWh: 32 cents is 0.32. Include applicable variable supply and delivery charges.

Check the arithmetic

Original cost = peak kWh × peak rate + off-peak kWh × off-peak rate. Here, 60 × $0.32 + 90 × $0.12 = $30. Moving 30 kWh changes the split to 30 peak and 120 off-peak: $9.60 + $14.40 = $24. Total energy remains 150 kWh.

Break-even against a flat tariff

With these example prices, the break-even peak share is ($0.20 − $0.12) ÷ ($0.32 − $0.12) = 40%. If more than 40% of the same energy falls in the peak window, the time-of-use energy charge is higher. This comparison assumes identical fees, taxes and consumption. It does not establish which actual plan is cheaper.

What to check on your bill

• Exact peak hours, weekends, holidays and seasonal schedules.
• Whether supply and delivery use the same rate windows.
• Demand charges, minimum charges, tiers and fixed monthly fees.
• Whether a changed schedule actually changes total consumption.

For three or more windows, calculate each window separately and add the charges. Use utility interval data when available. The tool models two windows only; it does not predict future rates.

Shift a load, not an essential service

Choose a flexible task whose manufacturer permits a different schedule. Do not switch off medical equipment, refrigeration or needed heating to chase the arithmetic. Changing time does not always preserve energy use: settings, temperature and operating mode can change consumption.

For watts-to-kWh conversion, use the appliance electricity calculator. For cycling devices, start with a measured energy log.

Method and sources

WattWorth · Published September 17, 2026. AI-assisted educational content; examples are calculated illustrations, not product testing. Editorial approach.

Energy calculations use watts ÷ 1,000 × hours = kWh. U.S. Department of Energy: Electricity 101 · DOE energy education: kWh formula