Who should use this guide
This framework is designed for drivers charging mostly at home, including owners comparing a standard residential plan against a TOU tariff, and recent EV buyers who want a realistic monthly charging budget. It also helps households where EV charging competes with other evening loads such as HVAC, electric cooking, or laundry.
Step 1: Map your utility tariff before running any math
TOU plans vary by utility territory. Before estimating savings, confirm the actual rate windows and terms in your utility tariff sheet or customer plan document.
- Peak and off-peak windows by weekday and weekend
- Seasonal definitions and schedule shifts
- Any fixed charges linked to TOU enrollment
- Rules for changing plans and switching back
Step 2: Convert driving into monthly charging kWh
Use a simple baseline: monthly miles divided by your EV efficiency (mi/kWh). This gives your approximate charging energy demand. Then split that energy between off-peak and peak windows based on your expected charging schedule.
Blended charging rate = (off-peak kWh x off-peak rate + peak kWh x peak rate) / total charging kWh
This blended rate is the number that should be compared with your current effective home charging cost.
Step 3: Build a charging schedule that survives real life
Many households underperform on TOU because schedules become too fragile. A robust setup includes a primary overnight window and a fallback window for late arrivals or unexpected mileage.
- Set a primary start time well inside off-peak hours.
- Keep a fallback start profile for irregular days.
- Reserve completion buffer before departure time.
- Review one week of charging logs and adjust once.
Step 4: Check household load interaction, not just EV load
Your EV is only part of the bill. If major home loads remain in peak windows, EV savings can be diluted. Review whole-home behavior before concluding that a TOU plan underperformed.
The most reliable method is a short interval-data audit. Pull your utility interval usage (15/30/60-minute chart), then compare those peaks with what ran in your home at the same time.
- Export 2 to 4 weeks of interval usage from your utility portal and mark TOU peak windows.
- Keep a 7-day device log for major loads: HVAC, electric water heater, dryer, oven/range, pool pump, and EV charging start times.
- Match recurring interval spikes to your device log to identify which loads are driving peak-period kWh.
- Run a one-variable test for one billing week: shift only one major load (for example dryer or water heater schedule) and compare peak-window kWh before and after.
This control loop gives you evidence-based adjustments instead of guessing why your TOU bill changed.
Step 5: Run a full billing-cycle validation protocol
Treat the first full billing cycle (often around 30 days) as a trial. Track these five metrics:
- Off-peak share of charging kWh
- Effective charging cost per kWh
- Total monthly EV charging spend
- Peak-period charging exceptions
- Total household bill movement
If results are mixed, adjust scheduling behavior first, then re-test before changing plans again.
When TOU plans are a poor fit
TOU may not be ideal if your routine forces frequent peak-hour charging, if your utility has narrow off-peak windows that conflict with your schedule, or if plan terms make reversions costly. In these cases, a stable standard plan can outperform a poorly matched TOU setup.