JJ Ben-JosephElectric vehicles draw electricity from the grid every time they are plugged in. Utilities often charge different rates depending on when power is used. During peak hours—typically afternoons and early evenings—the demand for electricity is highest, so the price rises. Off-peak hours, like late nights, are cheaper. Shifting your charging time can trim your energy bill without changing how much you drive.
Many drivers are uncertain how much they really save by using timers or smart chargers to delay charging until off-peak periods. This calculator quantifies the benefit using your daily energy use, local rates, and the portion of charging that can occur off-peak. By modeling different scenarios, you can decide whether investing in scheduling features or adjusting routines is worthwhile.
The fundamental cost calculation can be written in MathML as:
where E is monthly energy in kilowatt-hours, s is the standard rate, and p is the rate difference between off-peak and standard multiplied by the off-peak share. In plain words, we multiply energy by the blended rate to get total cost.
Suppose you drive enough each day to use 12 kWh and your utility charges $0.23 per kWh during the day but only $0.11 overnight. If you can shift 70% of your charging to the cheaper period and you drive 30 days per month, the calculator shows a monthly cost of:
All standard rates: 12 × 30 × 0.23 = $82.80.
With 70% off-peak: 12 × 30 × (0.7 × 0.11 + 0.3 × 0.23) = $56.52.
The difference is about $26.28 per month. Over a year, that’s more than $315 in savings just from scheduling.
The table generated above illustrates how costs change as more charging is moved off-peak. At 0% off-peak usage, you pay the full standard rate for all energy. At 100% off-peak, every kilowatt-hour is charged at the lower price. Many drivers can manage around 75% with a simple nightly charging routine.
In regions with large time-of-use rate spreads, off-peak charging can cut EV operating costs dramatically. Drivers who ignore rate schedules effectively pay a premium for convenience. Utility companies may eventually require smart charging to balance grid loads. Learning to charge during low-demand periods now prepares drivers for future incentives and helps stabilize the grid.
The formula is based on the idea that the total cost equals energy multiplied by a weighted average rate. Let f be the fraction of charging at the off-peak rate ro and (1 - f) at the standard rate rs. The blended rate is f ro + (1 - f) rs. Multiplying by total energy E gives E(f ro + (1 - f) rs). Rearranging terms yields E(rs + f(ro - rs)), which is what the calculator uses.
Charging habits vary widely. Some drivers plug in every night, others only when the battery is low. Time-of-use plans may include multiple tiers, seasonal adjustments, or even demand charges. The calculator simplifies these complexities into a single standard rate and off-peak rate. While this abstraction may gloss over nuances, it offers a clear baseline from which to evaluate decisions.
Real-world savings also depend on battery size and efficiency. A driver with a 60 kWh battery commuting 40 miles each day may use around 12 kWh daily, as in our example. Those with longer commutes or less efficient vehicles might consume 20 kWh per day, increasing potential savings. Conversely, drivers with short commutes may find that charging once every few days yields minimal off-peak benefits if they forget to schedule properly.
Off-peak windows vary. Some utilities consider 9 p.m. to 7 a.m. off-peak, while others specify midnight to 6 a.m. Many smart chargers allow setting a start time so charging completes before morning. A convenient strategy is to plug in after arriving home but delay charging until a specified hour. Even without a smart charger, many vehicles let you schedule charging via onboard software or mobile apps.
Another factor is battery health. Some experts advise charging to 80% daily to extend battery life, reserving 100% for long trips. Off-peak scheduling can make this easier: set the car to finish charging by departure time rather than starting immediately, preventing it from sitting at full charge for hours. This subtle benefit is not captured in the cost calculations but can lengthen battery lifespan and reduce long-term expenses.
Time-of-use plans are not universally available. In some regions, electricity is billed at a flat rate. In such cases, shifting charging times won’t affect cost, though it may still benefit grid stability. The calculator will show zero savings if standard and off-peak rates are equal, highlighting this limitation.
While the tool focuses on personal vehicles, fleet operators can apply the same principles at scale. A delivery company charging 50 vans overnight could see thousands in monthly savings by coordinating charging schedules. Installing smart chargers that automatically queue vehicles during the cheapest hours might pay for itself quickly.
Tables and Analysis: Beyond the simple table produced by the calculator, consider constructing your own scenarios. For example, compare months with higher driving (e.g., summer road trips) to quieter seasons. This can help determine whether a time-of-use plan is worthwhile year-round or only during certain months. Some utilities allow switching plans annually or even monthly; knowing your seasonal consumption patterns can help you choose the most economical option.
Another comparison is between different EV models. A large electric SUV might consume 30% more energy than a compact sedan for the same miles driven. By entering higher daily kWh figures, you can see how vehicle choice influences savings. Coupling this with data from our EV Charging Time Calculator or the EV Fast Charging Wait Time Calculator provides a fuller picture of operating costs.
Utility programs sometimes offer rebates for installing smart chargers that can be remotely managed. If you are considering such hardware, use the calculator to project savings and compare them to equipment costs. Pair it with our Home Battery Time-of-Use Arbitrage Calculator to explore storing cheap overnight power for later use.
This tool assumes a constant daily driving energy and consistent rates throughout the month. It doesn’t account for tiered pricing where rates increase after a certain usage threshold. Taxes and fixed fees are excluded, as they usually apply equally regardless of charging time. The model also assumes charging efficiency is the same during all periods, though small differences may exist due to ambient temperatures or charger performance.
We also presume that you can actually shift the specified portion of charging to off-peak hours. Some drivers rely on workplace or public chargers that may have fixed pricing independent of time. In those cases, off-peak savings at home might be less significant.
By quantifying off-peak savings, this calculator empowers EV owners to make informed choices about when to charge. Even modest scheduling adjustments can reduce costs and environmental impact. Use it regularly as rates or driving patterns change, and explore related tools to optimize your electric vehicle ownership experience.
Related calculators: EV Charging Time Calculator and EV Fast Charging Wait Time Calculator.
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