How to use this calculator
A time-of-use plan can help only when enough consumption happens in lower-priced hours. This calculator isolates energy charges so you can test peak-use shares before changing tariffs.
- Enter monthly kWh from a representative bill.
- Estimate the share used in the peak window.
- Copy exact peak, off-peak, and flat rates.
FORMULA
The math behind the estimate
peak kWh × peak rate + off-peak kWh × off-peak rate = time-of-use energy cost.
Worked example
For 900 kWh with 35% at $0.32 and 65% at $0.12, TOU costs about $171 versus $162 at a flat $0.18 rate.
Change the defaults to model your home. The result is an estimate, not a guaranteed bill or savings promise.
How to read the result
Use the estimate to compare scenarios and find the inputs worth measuring more carefully. Utility bills can include fixed charges, taxes, delivery fees, minimums, tiers, and demand charges that are not fully represented by a simple energy rate.
Assumptions and limitations
- Only two time periods are modeled.
- Fixed, demand, seasonal, and tier charges are excluded.
- Both plans use the same total kWh.
Climate, equipment condition, installation, controls, and household behavior can materially change results. Verify consequential installation and purchasing decisions with qualified providers.
Practical savings context
Shift flexible loads such as EV charging, laundry, dishwashing, and water heating only when safe and practical.
SOURCE
Data and methodology
U.S. Energy Information Administration — Electricity Prices
Rate context accessed August 2026. Geographic scope: United States. Last reviewed: August 6, 2026.
WattMeasure uses the source to frame the method and assumptions; your editable inputs determine the displayed result.
QUESTIONS
Peak vs off-peak FAQ
How accurate is this time-of-use rate estimate?
It is a planning estimate based on the values you enter. Actual power draw, cycling, utility charges, climate, and equipment condition can change the result.
Should I use the default electricity rate?
Your own marginal or all-in supply rate is better. Check a recent bill or your utility's published rate schedule.
Does this include taxes and utility fees?
Only when they are reflected in the rate you enter. Fixed monthly charges are not included because they usually do not change with one appliance's usage.
Last reviewed August 6, 2026 · Data update policy