EV off-peak charging savings

The arithmetic is deterministic and identical in the free browser tool and the API path, so home energy advisors, fleet total-cost worksheets, and personal spreadsheets never disagree on the same inputs.

How peak and off-peak prices turn into annual EV savings

Utilities that publish time-of-use rates list at least two prices per kilowatt-hour: a higher peak rate for high-demand windows (often late afternoon and early evening) and a lower off-peak rate for overnight or mid-day shoulder periods. When the share is zero, nothing is shifted and savings are zero. Real bills may still include fixed service fees, demand charges, or seasonal rate tables that this calculator does not model; treat the result as the energy-only savings from shifting EV charging, not a full utility bill forecast. An electric vehicle that charges entirely during the peak window pays annual_kwh times peak_price for the year. The same vehicle that moves a fraction off_peak_share of that energy into the cheap window pays a mixed annual cost equal to annual_kwh times the weighted average of the two rates. Subtracting the mixed cost from the peak-only cost yields annual savings of annual_kwh times off_peak_share times the price spread (peak minus off-peak). When off_peak_share is one, every kilowatt-hour is charged off-peak and savings equal the full spread times yearly energy. The response also reports monthly_savings as annual_savings divided by twelve, savings_per_kwh as the effective unit discount after the share is applied, peak_annual_cost, off_peak_annual_cost for a full off-peak baseline, and mixed_annual_cost for the partial shift you described.

Input contract, validation, and reading the response

Currency is informational only: the service does not convert between currencies, so keep both prices in the same unit you display. Missing required fields, empty strings, and non-finite values name the field in the error message. Example: three thousand six hundred kilowatt-hours per year, peak thirty-two cents, off-peak twelve cents, and full off-peak share yields seven hundred twenty currency units of annual savings, because thirty-six hundred times zero point two equals seven hundred twenty. POST a JSON body with three required non-negative finite numbers: annual_kwh (aliases yearly_kwh, annual_energy_kwh, kwh_per_year) for yearly charging energy in kilowatt-hours; peak_price (aliases peak_price_per_kwh, on_peak_price, peak_rate) for the on-peak tariff per kWh; and off_peak_price (aliases off_peak_price_per_kwh, offpeak_price, off_peak_rate) for the cheap-window tariff per kWh. Optionally send off_peak_share between zero and one inclusive (default one) for the fraction of annual energy you can schedule off-peak, and currency as a string label such as USD or EUR. Negative annual energy or negative prices fail with invalid_input and are not billed, because a negative tariff or energy volume is not a meaningful yearly plan. An off_peak_share outside the closed unit interval is likewise rejected. On success the body echoes the resolved inputs, reports price_spread as peak_price minus off_peak_price (which may be negative if the cheap rate is entered higher than the peak rate), and returns the cost and savings fields rounded for stable cross-runtime comparison. Pair the response with your own charger schedule or vehicle telematics if you need to estimate what share is realistic; this endpoint only multiplies the share you provide.

Where off-peak EV savings estimates earn their keep

Households choosing between a flat residential rate and a time-of-use plan use this EV off-peak charging savings calculator to see whether overnight charging alone covers the plan switch over a commuting year. Fleet managers batch depot vehicles with depot peak and off-peak depot tariffs to build transparent energy line items for total cost of ownership reports without inventing a blended rate that hides the overnight discount. Keep requests small, pin rounded money fields in tests, and re-run when the utility updates seasonal peak windows so next year’s estimate tracks the tariff you actually pay. Home energy advisors and solar-plus-storage installers plug measured or estimated annual kWh from the vehicle or a wallbox, then vary off_peak_share to show partial automation versus manual schedules. Combine annual_savings with travel.ev_trip_cost when you need both per-trip energy cost at a single rate and the yearly benefit of shifting the whole charging stack to off-peak hours.