EV Time-of-Use Charging Savings Calculator

Stephanie Ben-Joseph headshotEdited by: Stephanie Ben-Joseph

Introduction: Why EV charging time affects your electricity bill

Time-of-use (TOU) electricity plans charge different prices for the same EV kilowatt-hours depending on when charging occurs. This EV charging calculator compares a flat electricity price with a schedule split among super off-peak, regular off-peak, and peak periods. It is designed to show whether a charging routine that fits your driving needs is likely to cost less than a flat-rate alternative, rather than assuming that every TOU plan is automatically cheaper.

The estimate first turns annual driving into monthly energy drawn from the grid using the vehicle’s kWh-per-mile efficiency and the charging-loss percentage you enter. It then assigns that energy to the super off-peak and regular off-peak shares you specify; the balance is treated as peak charging. With the entered electricity prices, the calculator produces flat-rate and TOU monthly and annual costs. It shows separate TOU results for the standard and managed monthly demand charges because either charge can affect the plan comparison.

This EV TOU comparison also estimates charging emissions. Enter peak and off-peak emissions intensities from a utility, grid operator, or other source appropriate for your area. The calculator applies the off-peak intensity to both off-peak categories and compares the resulting annual emissions with an all-peak charging baseline. It measures the timing-related difference in charging emissions, not the full lifecycle emissions of the vehicle or electricity system.

How to use: How the EV time-of-use calculation works

For an EV charging estimate, the model derives monthly grid energy from annual miles, vehicle efficiency, and charging losses:

Emonth = M 12 × k × ( 1 + λ )

Here, M is annual miles, k is vehicle efficiency in kWh per mile, and λ is the charging-loss percentage expressed as a decimal. The entered super off-peak and regular off-peak percentages cannot exceed 100% together. Any unassigned portion of EV charging is priced and counted as peak-period charging.

For EV charging on a flat plan, the monthly energy cost is monthly energy multiplied by the flat $/kWh rate. For the TOU plan, the calculator multiplies each scheduled energy share by its super off-peak, regular off-peak, or peak rate, then adds the selected monthly demand charge. It displays outcomes using both the standard and managed demand-charge entries. Annual costs are monthly costs multiplied by 12, and each annual savings figure is the flat-rate annual cost minus the corresponding TOU annual cost.

The breakeven result identifies the regular off-peak share needed for the TOU energy rate to equal the flat rate while holding the entered super off-peak share fixed. It does not include either demand charge, so use the full annual-cost rows when demand charges apply. The result is limited to the regular off-peak share still available after the super off-peak share. Carbon estimates multiply annual charging energy in each time period by the entered peak or off-peak intensity, then compare that total with charging all of the same energy at peak intensity.

Worked example: EV charging on the displayed TOU schedule

Using the form’s displayed values, a driver travels 12,000 miles annually in an EV rated at 0.28 kWh per mile and enters 12% charging losses. The calculator’s monthly grid-energy requirement is 313.60 kWh. With 20% of charging in the $0.08 super off-peak period, 50% in the $0.12 regular off-peak period, and the remaining 30% at the $0.32 peak price, the TOU energy cost is $53.94 per month. The flat-rate energy cost at $0.18/kWh is $56.45 per month.

With both displayed demand-charge fields set to zero, those figures annualize to about $647.27 for TOU charging and $677.38 on the flat rate, a difference of about $30.11 per year. At the displayed emissions inputs, the all-peak baseline is about 1.69 metric tons CO2e annually, while the scheduled TOU charging estimate is about 1.35 metric tons. These results change directly when rates, charging shares, losses, or emissions intensities change, so they should be treated as a scenario based on the values entered rather than a utility-bill forecast.

Input tips and validation for EV TOU rates

For a useful EV time-of-use estimate, use annual mileage and efficiency values that reflect your vehicle and driving pattern. Enter charging losses as the percentage requested by the form; the calculator converts that percentage to a decimal before increasing grid energy. Check your utility’s current rate schedule carefully, including the hours that define peak, off-peak, and super off-peak service. If your plan has no super off-peak price, enter zero for that share and use the applicable off-peak rate for the rest of your scheduled charging.

The calculator prevents super off-peak and regular off-peak shares from exceeding 100% in total. It does not infer a charging schedule from plug-in times, so the percentages should represent the energy you realistically expect to receive in each period. Demand charges are often absent from residential bills but may be relevant to fleet or commercial charging. Enter them only when they apply to the plan being evaluated, and use the two fields to compare a standard charge with a managed-charging alternative.

Comparing EV charging scenarios

To compare EV TOU scenarios, change one scheduling or rate assumption at a time and review the energy-cost, demand-charge, and annual-savings rows together. Moving energy from peak to regular off-peak reduces the energy-cost component when the off-peak price is lower. Moving energy into super off-peak can reduce it further when that price is lower still. A monthly demand charge, however, is added after the energy calculation and can outweigh a favorable per-kWh rate difference.

Use the breakeven share as a scheduling benchmark rather than as a guarantee of bill savings. It is calculated from the flat, peak, regular off-peak, and fixed super off-peak rates and shares, without demand charges. If the required regular off-peak share is outside the portion of charging not already assigned to super off-peak, that rate combination cannot reach an energy-only breakeven with the current super off-peak setting. The annual cost rows remain the appropriate comparison when either demand charge is nonzero.

Understanding EV charging carbon implications

The emissions portion of this EV charging calculator focuses on when grid energy is delivered. It treats super off-peak and regular off-peak charging with the same off-peak emissions intensity because the form provides one off-peak intensity input. Peak charging uses the separate peak intensity. If the values are identical, shifting charging periods produces no modeled emissions change even if it changes electricity cost.

The all-peak baseline is a deliberately simple reference: it applies the peak intensity to all annual charging energy. The reported emissions avoided are the difference between that baseline and the schedule entered in the form. Actual grid emissions can vary by hour, season, and location, and utility rate periods do not always align with the grid’s marginal-emissions periods. For that reason, local time-specific data is more informative than a broad regional average when emissions timing is a key decision factor.

Limitations and next steps for TOU plan decisions

This EV TOU tool is a planning estimate, not a replacement for reading a utility tariff or bill. It uses constant entered rates, one vehicle, and a monthly energy average. It does not model seasonal rate changes, taxes, fixed customer charges, minimum bills, critical-peak events, solar exports, battery storage, or demand charges based on a measured interval maximum. Those details can materially change the best plan for a household or fleet.

Before switching an EV to a TOU rate, compare the calculator’s assumptions with your utility’s plan documents and your charger’s scheduling options. A delayed-start setting, a smart charger, or a managed-charging program may help align actual charging with lower-priced periods, but only if the vehicle is still ready when needed. Revisit the inputs when mileage, rates, or your charging routine changes.

Formula: how the EV TOU cost estimate is built

The EV charging estimate starts with monthly grid energy and then applies the entered schedule shares and rates. Keep annual driving distance in miles, vehicle efficiency in kWh per mile, charging losses and schedule shares as percentages, electricity prices in dollars per kWh, and demand charges in dollars per month. Before either monthly demand charge is added, the calculator’s TOU charging energy cost is:

CTOU=Emonth×(s×Rsuper+o×Roff+(1−s−o)×Rpeak)

The regular off-peak energy-only breakeven calculation, with the super off-peak share held fixed, is:

o=Rflat−Rpeak−s(Rsuper−Rpeak)Roff−Rpeak

Quantify how much you could save by switching an electric vehicle to a time-of-use rate plan and charging during off-peak hours.

Arcade Mini-Game: EV Time-of-Use Charging Savings Calculator Calibration Run

Use this quick arcade run to practice separating useful scenario inputs from common planning mistakes before you rely on the calculator output.

Score: 0 Timer: 30s Best: 0

Start the game, then use your pointer or arrow keys to catch useful inputs and avoid bad assumptions.

Status messages will appear here.