How this EV charging time calculator works
The simple answer to “how long does it take to charge?” (battery kWh divided by charger kW) is wrong in both directions. It ignores that the car, not the charger, often sets the limit, that AC charging loses energy in the on-board charger, and that DC fast charging follows a taper curve: full power in the middle of the battery, much less near the top. This calculator models all three.
It integrates the session in 0.5% state-of-charge steps. At each step it works out the power the battery can actually accept and how long that slice of energy takes, then adds the slices up. For AC charging, power is the lower of the charger rating and your car’s on-board charger, multiplied by the charging efficiency, and it eases off above 90%. For DC charging, power is the lower of the charger rating and the car’s peak DC power multiplied by a taper factor and a battery-temperature factor. You can pick a typical curve (taper starting near 50%) or a flatter curve typical of 800-volt cars (taper starting near 65%).
The formula
DC: P(SoC) = min( P_charger , P_car,peak × taper(SoC) × f_temp ) AC: P(SoC) = min( P_charger , P_onboard ) × η_AC × (1 above 90% → 0.3 at 100%)
taper: 1.0 up to ~50% (65% flat curve) → 0.5 at 80% → ~0.08 at 100% Range added = energy added ÷ consumption × 100
Temperature factors are 1.0 for a warm battery, 0.8 for a mild one and 0.5 for a cold, non-preconditioned pack.
Worked example
The defaults model a family EV with a 75 kWh usable battery, an 11 kW on-board AC charger and a peak DC rate of 170 kW, charging from 10% to 80% on a 150 kW DC charger with a warm battery.
The session adds 0.70 × 75 = 52.5 kWh, about 292 km of range at 18 kWh/100 km. Because the charger (150 kW) is below the car’s peak (170 kW), the car draws the full 150 kW from about 11% to the mid-50s. Beyond that the taper pulls the car’s acceptance below the charger rating, and by 80% the car takes roughly 85 kW. Average power over the session is 136 kW, so the charge takes about 23 minutes, adding range at roughly 750 km per hour. Including about 5% in-car losses, 55.3 kWh is billed — €32.60 at €0.59/kWh.
The comparison table shows the same 10→80% session elsewhere: about 63 minutes on a 50 kW charger, 5 h 18 min on an 11 kW wallbox, 7 h 53 min on a 7.4 kW wallbox and more than 25 hours on a domestic socket. A 22 kW post is no faster than 11 kW here because the car’s on-board charger caps AC at 11 kW, and a 350 kW charger saves only a minute because the car, not the charger, is the bottleneck.
How to read the results
- Charging time is the headline for your chosen SoC window.
- Average vs peak power: a big gap means you spent much of the session in the taper. Starting lower and stopping earlier raises the average.
- The verdict says what limits you: the charger or the car. Paying for a faster charger is pointless if the car is the limit.
- SoC vs time chart: the line bends over near the top; that bend is the taper.
- Power vs SoC chart shows the charging curve itself.
- Session cost uses the price in the advanced settings; see the EV charging cost calculator for monthly totals.
Typical values
| Charger | Real power to battery | 10→80% of 75 kWh | Range added per hour (18 kWh/100 km) |
|---|---|---|---|
| Domestic socket 2.3 kW | ~2 kW | 25+ h | 10–12 km |
| Wallbox 7.4 kW (1-phase) | ~6.7 kW | ~8 h | ~37 km |
| Wallbox 11 kW (3-phase) | ~10 kW | ~5.3 h | ~55 km |
| DC 50 kW | 45–50 kW | ~1 h | ~270 km |
| DC 150 kW | 100–140 kW avg | 20–30 min | 600–750 km |
| DC 350 kW (800 V car) | 150–230 kW avg | 15–20 min | 800–1,200 km |
Tips to charge faster
- Arrive low, leave at 80%. The fastest part of the curve is between roughly 10% and 60%. Two short stops beat one long stop to 100%.
- Pre-condition in winter. Set the charger as the destination in the car’s own route planner so it warms the battery; a cold pack can halve DC speed.
- Match the charger to the car. A 350 kW post gives no benefit to a car limited to 100 kW, and a 22 kW AC post no benefit to an 11 kW on-board charger.
- At home, 7–11 kW is plenty. Overnight, even 7.4 kW refills a typical day’s driving in two to three hours.
- Avoid shared-power cabinets when possible: some DC sites split power between two cars.
Limitations
The DC curve is a generic shape. Real curves differ by model, chemistry (LFP packs often hold power higher), software version, cell temperature and charger behaviour; some cars step down in plateaus rather than linearly. Charging below 10% can also be slower than modelled. AC charging assumes a constant grid voltage and ignores the current limits that some wallboxes apply under load management. Use the result as a planning estimate, and check model-specific charging curves from independent tests for precise road-trip planning.
Method & assumptions
The session is integrated in 0.5% SoC steps: Δt = (battery kWh × ΔSoC) ÷ P(SoC). For DC, P = min(charger kW, car peak kW × taper(SoC) × temperature factor); the taper holds peak power to ~50% (65% for flat-curve 800 V cars), falls linearly to 50% of peak at 80% and to ~8% at 100%. For AC, P = min(charger, on-board charger) × efficiency, reduced above 90%.
Frequently asked questions
How long does it take to charge an electric car?
Why does EV charging slow down after 80%?
Does a 22 kW charger charge faster than an 11 kW one?
How long does it take to charge an EV with a normal 3-pin plug?
Does cold weather affect charging time?
How many km of range do I get per hour of charging?
Sources & references
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