Time of Use vs Flat Rate Electricity: Compare Your Whole Bill

To compare time of use vs flat rate electricity, price your whole household's usage under both plans. A cheap overnight rate helps only when enough electricity is used in those hours. Higher peak prices, fixed charges and other plan rules can outweigh that saving.

This is a method for comparing U.S. residential electricity plans, not a recommendation for a particular utility. Availability, peak windows and enrollment conditions vary. Use the current tariff, which is the utility's official schedule of prices and rules, for your service address.

Identify the plan rules before comparing prices

A flat-rate plan generally charges the same energy price throughout the day, though the price may still change by season or usage tier. A time-of-use plan charges different energy prices in defined time windows. A fixed contract price and a flat hourly price describe different things; don't assume the word “fixed” answers both questions.

The U.S. Energy Information Administration's electricity-pricing overview explains that time-based prices and other pricing structures differ. Your own tariff controls the comparison, rather than a national average or a neighbor's plan.

• Which hours are peak, off-peak or another price band?
• Do weekends, holidays and seasons have different windows?
• Are there fixed monthly charges, minimum bills or enrollment fees?
• Does the plan include demand charges based on a measured power peak?
• How are solar exports, credits and taxes calculated?
• Can you leave the plan, and are there limits on switching again?

Use interval data where you can

Interval data records electricity use in small time blocks, such as hourly or shorter readings. Request or download it through your utility's normal customer tools. You don't need to share account credentials with an installer to ask for a written comparison.

Match the readings to each plan's clock, time zone and seasonal dates. Check how daylight saving time is handled. A monthly total alone cannot tell you how much electricity fell in an expensive afternoon window.

Use a full year when available. Heating, cooling and daylight can change when the house uses power. Check for estimated bills, missing intervals, an unusually long absence or a recent change in occupancy before treating the data as representative.

Calculate a whole-bill example

Here is a deliberately simplified, hypothetical month with 1,000 kWh of household use. The flat plan charges $0.18 per kWh plus $15. The time-of-use plan charges $0.12 off-peak and $0.32 at peak, plus $20. These are invented prices, not current utility offers. This example excludes taxes, tiers, demand charges, exports and other adjustments.

Same monthly energy, different timing

Usage pattern	Flat plan	Time-of-use plan
200 kWh peak, 800 kWh off-peak	1,000 × $0.18 + $15 = $195	200 × $0.32 + 800 × $0.12 + $20 = $180
400 kWh peak, 600 kWh off-peak	$195	400 × $0.32 + 600 × $0.12 + $20 = $220

In the first pattern, time-of-use saves $15 that month. In the second, it costs $25 more. The house uses the same total energy in both examples; the timing changes the bill.

For these exact simplified prices and 1,000 kWh total, the plans break even at 275 peak kWh, or 27.5% of usage. That threshold will change with the monthly total, fixed charges and every additional billing rule. It is not a general switching rule.

Test what you can realistically move

List flexible loads separately from essential ones. An EV that stays plugged in overnight may offer flexibility. Cooking, hot-water needs and a heat pump maintaining a safe indoor temperature may not move as easily. Don't assume every appliance can be delayed without affecting the household.

Use the EV charging-cost worksheet for the vehicle portion, then add it back into the whole-house plan. Include extra EV use only if it isn't already in the historical readings. For future equipment, ask the installer to explain the expected seasonal usage profile rather than assigning a whole annual estimate to cheap hours.

🛑 Keep necessary heating, cooling, medical equipment and other essential services operating safely. Follow the equipment's instructions; don't disable protection or force unsafe schedules to avoid a peak rate.

Keep solar and battery accounting separate

Solar can reduce imports in some hours, while export credits apply to electricity sent to the grid. Don't value every solar kWh at the highest retail rate if it would actually receive a different export credit. The home solar guide explains the wider system and utility questions.

A battery shifts energy with losses and operating limits. Compare what it costs to charge, what purchases it avoids and whether reserve settings leave energy available for that purpose. Equipment costs, wear and program restrictions still matter. See the home battery storage guide before treating a rate gap as guaranteed profit.

Compare the year and check the first bills

1. Calculate the same historical intervals under each available plan.
2. Add each plan's fixed charges and other applicable bill components.
3. Test a realistic schedule change and a case where you can't make it.
4. Add future loads once, with their expected timing.
5. Check annual totals and difficult seasonal months, not just the best month.

After switching, check the billed plan, time windows and actual usage. If the result differs, look for timing errors, seasonal changes or missing charges before assuming an appliance failed. Use energy-savings measurement to separate lower consumption from lower prices.

Conclusion

The better plan depends on when your home uses electricity and how the entire bill is calculated. Compare a full year, test realistic schedules and keep essential household needs ahead of rate optimization.

Return to the upgrade-costs hub or explore our Energy Efficiency guides for equipment and budgeting decisions.

Scott Harding

Scott is the main author of DIY Home Comfort. Learn more about the team and our approach on the About page.