SolarToolsHow This Tool Works
The Time-of-Use (TOU) Rate Optimizer tells you how much money you can save by shifting when you run major appliances. If your utility offers a TOU plan — and most do, especially in California, New York, Massachusetts, Hawaii, and South Africa — electricity costs 2–4× more during peak hours than off-peak. Running your dishwasher at 7pm versus 11pm can cut its energy cost by 60%. Multiply that across laundry, EV charging, water heating, and pool pumps, and the annual savings can exceed $400 with zero change in lifestyle.
The calculator loads real peak and off-peak rates for 24 regions across the US and South Africa. Enter how often you run each shiftable load, and it estimates the daily shiftable kWh, the rate spread in your area, and the realistic annual savings assuming you shift 80% of those loads. The 80% figure accounts for the fact that some loads (cooking, lighting in the evening) can't be moved.
The recommended schedule panel shows the optimal time window for each appliance type based on your region's peak hours. For most US regions peak runs 4pm–9pm; for South Africa it's typically 6am–9am and 5pm–8pm (load-shedding-adjacent). The cheapest window is almost always 11pm–6am.
If your savings come back small, you're either already on a flat-rate plan (in which case TOU isn't worth switching to), your rates are already cheap (Pacific Northwest), or you don't have enough shiftable load. Pair this with the EV Charging Cost Calculator to see how much TOU specifically helps EV owners.
- Pick your region. The dropdown loads real peak, off-peak, and peak-hour-window data for 24 utilities across the US and South Africa.
- Be honest about appliance usage. Count your actual weekly loads of laundry, dishwasher cycles, etc. Don't overestimate.
- EV kWh/week = daily miles × 7 / efficiency. 30 miles/day at 3.5 mi/kWh = 60 kWh/week. Long commutes: 150+.
- Pool pump hours/day = your actual pump runtime. Variable-speed pumps run longer at lower wattage but use similar total kWh.
The result assumes 80% of shiftable loads actually get shifted — realistic for households with smart appliances, EV chargers with scheduling, and timer-equipped water heaters. Without those, expect 50–60% shift.
When to Use This Calculator
How TOU pricing works
Utilities price electricity by the cost of generation at the moment it's produced. Evening peak (4pm–9pm) is when demand is highest and the most expensive peaker plants (often natural gas) get fired up. Overnight (11pm–6am) demand is lowest and base-load plants (nuclear, wind, hydro) are running underutilized. TOU pricing passes that cost difference to consumers. A peak rate of $0.42/kWh and off-peak of $0.18/kWh isn't a markup — it reflects what the utility actually pays.
What's shiftable and what isn't
Easily shiftable: dishwasher (delay start), laundry (run overnight), EV charging (schedule in app), water heating (timer on tank), pool pump (timer), slow cooker, robot vacuum. Hard to shift: cooking dinner, evening lighting, refrigerator, AC during heatwaves, internet/WiFi. Plan around the easy 80% — the hard 20% will eat whatever peak-rate kWh it eats.
The 80% shift assumption
Real-world studies (LBNL, EPRI) show that even with smart appliances and timers, households achieve 60–80% shift of technically-shiftable loads. Forgetting to set a timer, needing a quick wash during peak, or having guests who run the dryer at 7pm all eat into the theoretical maximum. The calculator uses 80% as a realistic upper bound.
When TOU isn't worth it
Three cases: (1) you're on a flat-rate plan and the TOU alternative doesn't have a meaningful peak/off-peak spread, (2) you're home all day with kids and cooking loads you can't shift, (3) your household uses very little electricity overall. In each case, switching to TOU could actually increase your bill. Run the numbers honestly before switching plans.
Batteries + TOU = supercharged savings
If you have a home battery, you can charge it during off-peak and discharge during peak, capturing the full rate spread on every kWh. This is called arbitrage. The Battery ROI Calculator includes this case — for California and Hawaii customers, TOU arbitrage is often the only economic case for batteries.
Frequently Asked Questions
TOU is a rate plan where electricity costs more during high-demand hours (typically 4–9pm) and less during low-demand hours (11pm–6am). The peak/off-peak spread is typically 2–4×, reflecting the actual cost of generation at different times.
If you can shift at least 30% of your load to off-peak hours, TOU usually saves money. If you work from home, have kids, or cook extensively during peak hours, you may be better off on a flat-rate plan. Run this calculator with your actual usage to compare.
Pick the closest match in your country — peak/off-peak windows are similar within each grid. Or enter your actual rates manually by checking your utility's website. The math is the same; only the rate numbers differ.
Substantial. At $0.30 peak vs $0.10 off-peak, charging 60 kWh/week overnight saves $12/week or $624/year. EVs are the single biggest TOU win because their load is large and 100% shiftable.
Yes — the water heating input assumes you can install a timer that heats the tank during off-peak and stores hot water for the day. Electric tanks lose about 1°C/hour standing, so a 200L tank heated to 60°C stays above 50°C for 12+ hours.
Further Reading
Deep-dive articles and guides related to this calculator.
Understanding Time-of-Use Electricity Rates: Save Money by Shifting Load
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Energy & Solar Glossary
Plain-English definitions of every term used in this calculator and across the site.