About the Time-of-Use Rate Calculator
This time-of-use rate calculator compares your monthly electricity bill on a time-of-use (TOU) plan — where power costs more in the late-afternoon and evening peak and less overnight — with a standard flat-rate plan. Enter your monthly kWh, how that usage splits across peak, mid-peak and off-peak hours, and the prices from your utility’s rate sheet.
It is built for households deciding whether to switch plans, EV owners who charge overnight, and anyone with a battery, heat pump water heater or smart appliances that can shift load. The "shift" input shows how much you could save by moving part of your peak use, such as laundry or dishwashing, to off-peak hours.
Your usage split can be read from a smart-meter download or your utility’s online account. If your plan has no mid-peak period, set its share to zero. Taxes, tiered pricing and demand charges are not included, so compare the energy portion of your bill.
With the default inputs, the monthly savings on tou (negative = tou costs more) is −$10.80. Change any value above to recalculate instantly.
How to use the time-of-use rate calculator
- 1Enter your average monthly kWh from a recent bill.
- 2Estimate the share of use in the peak and mid-peak windows (from smart-meter data if you have it).
- 3Enter the TOU prices and the flat price from your utility’s rate sheet.
- 4Add each plan’s fixed monthly charge.
- 5Try the shift slider to see what moving laundry, dishes or EV charging off-peak would save.
Formula and method
Your monthly usage is split into peak, mid-peak and off-peak kWh using the shares you enter, and each block is priced at its own rate. Any shifted usage is moved from the peak block to the off-peak block, keeping total kWh the same. The flat bill is simply total kWh times the flat price plus its fixed charge.
The break-even on-peak share solves TOU = Flat for the peak fraction p, holding the mid-peak share m constant: p = ((Flat − F_tou) ÷ kWh − m × R_mid − (1 − m) × R_off) ÷ (R_peak − R_off). If your peak share is below this value, the TOU plan is cheaper.
- F
- Fixed monthly customer charge of each plan
- R
- Energy price per kWh for each period or plan
- p, m
- Shares of monthly use in the peak and mid-peak windows
Worked examples
Typical home with 30% peak use
900 kWh split 30/20/50 costs 270 × $0.38 + 180 × $0.24 + 450 × $0.14 = $208.80 plus $12, or $220.80 on TOU, versus $210 on the flat rate. TOU would only win if the peak share fell below 25%.
Shifting 40% of peak use to overnight
Moving 40% of the 270 peak kWh (108 kWh) to off-peak leaves 162 kWh at $0.38 and raises off-peak use to 558 kWh. The TOU bill drops to $194.88, saving $15.12 a month or $181 a year compared with the flat rate.
EV owner charging overnight
With 1,400 kWh a month and only 15% on-peak, the TOU bill is $12 + 1,400 × $0.191 = $279.40, against $320 on the flat rate — a $40.60 monthly saving. TOU stays cheaper as long as the peak share is below about 27%.
Frequently asked questions
Is a time-of-use plan worth it?+
It is worth it if you can keep most of your usage outside the peak window, typically late afternoon and early evening. Households that charge an EV overnight, run laundry and dishwashers late, or have a home battery usually save; those who use a lot of air conditioning in the evening often pay more.
What are typical time-of-use peak hours?+
Many US utilities set the peak window somewhere between 3 pm and 9 pm on weekdays, often 4–9 pm, with off-peak overnight and on weekends. Exact hours and seasons vary by utility, so check your rate sheet.
How do I find my peak usage share?+
Most utilities with smart meters let you download hourly or 15-minute usage data from your online account. Add up the kWh used in the peak hours and divide by your total monthly use.
What loads are easiest to shift off-peak?+
EV charging, dishwashers, washing machines, dryers, pool pumps and water heaters can usually be scheduled for overnight or midday. Pre-cooling or pre-heating the house before the peak window can also cut peak air-conditioning use.
Do time-of-use plans help with solar panels?+
It depends on how exports are credited. If your utility credits exports at TOU prices, solar output in the afternoon can be valuable; under newer net-billing rules, a battery that stores daytime solar for the evening peak often gives the most benefit.