Estimate EV charging time remaining from battery size and charger power
Know when the car will be ready: a 75 kWh battery going from 20% to 80% needs 45 kWh, which takes about 4 hours and 5 minutes on an 11 kW charger. The energy needed is shown too. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Capacity kwh
- 75
- Current pct
- 20
- Target pct
- 80
- Charger power kw
- 11
- Charge difference pct
- 60
- Energy required kwh
- 45
- Hours
- 4.090909
- Minutes
- 245.454545
This EV charging time estimator calculates how long an electric vehicle should take to move from its current battery percentage to a higher target percentage. Enter the battery capacity in kilowatt-hours, the present and desired states of charge, and the charger power in kilowatts. The result shows the energy required and the estimated duration in hours and minutes. It is an ideal constant-power estimate, useful for planning and comparison rather than a promise of an exact departure time.
Enter values that describe the charging session
Start with the vehicle battery's nominal capacity in kilowatt-hours. Then enter the percentage displayed now and the higher percentage you want to reach. Finally, provide the charger power available to the vehicle in kilowatts.
Use the power the car can actually accept, not necessarily the maximum number printed on the charging station. For example, a 150 kW station does not deliver 150 kW to a car whose DC charging limit is 80 kW. Likewise, an 11 kW home unit may be limited by the vehicle's onboard AC charger or the electrical installation.
The target must be greater than the current percentage because this calculator estimates charging time remaining, not energy consumption while driving or discharging. Percentages must stay between zero and one hundred. Keeping every value in the stated units avoids a common thousand-fold error caused by mixing watts with kilowatts or watt-hours with kilowatt-hours.
Understand the calculation and the returned values
The calculation first finds the requested increase in state of charge by subtracting the current percentage from the target percentage. It multiplies that percentage difference by the full battery capacity to estimate the energy that must enter the battery. A 75 kWh pack moving from 20% to 80%, for example, requests 45 kWh because sixty percent of 75 is 45.
The estimated hours are then found by dividing required energy in kilowatt-hours by charger power in kilowatts. The response also converts that duration to minutes and reports the charge difference and required energy, making the result easy to audit. Values are rounded to six decimal places for stable, reusable output.
This is a deterministic calculation: identical inputs always produce identical results, and it uses no network lookup, live vehicle data, randomness, or clock. The method and formula fields explicitly identify the constant-power model so downstream systems can preserve the assumption alongside the estimate.
Allow for real-world charging conditions
Actual sessions often last longer than the ideal estimate. Charging power is rarely constant from plug-in to departure: a cold or hot battery may accept less power, the vehicle can taper its charging rate as the battery fills, and a shared station may divide capacity among several cars. Conversion losses also mean the energy drawn from the grid can exceed the energy stored in the battery.
This calculator deliberately does not invent an efficiency factor or a charging curve because neither can be inferred reliably from the four inputs. Treat the answer as a clean baseline for comparing chargers, planning a rough stop, testing an application, or checking whether a quoted duration is plausible. For a conservative departure plan, add a buffer based on experience with the specific vehicle and site.
Targets near 100% usually need a larger buffer because tapering is strongest near full charge. Battery capacity may also differ from usable capacity, so prefer the usable figure when the manufacturer publishes it and your goal is closer real-world planning.
What you can do with it
Plan a home charging window
Estimate whether an overnight AC session can raise the vehicle from its current charge to the desired morning target.
Compare charger power levels
Run the same battery and percentage inputs with different charger outputs to compare ideal session durations.
Validate an EV application
Use deterministic energy and time fields as a reference when testing dashboards, trip planners, or charging workflows.
FAQ
Does the estimate include charging losses?
No. It uses ideal battery energy and constant charger power because no efficiency or loss input is provided.
Why can real charging take longer?
Battery temperature, charger sharing, vehicle limits, conversion losses, and power tapering can all reduce the average charging rate.
Should I enter the station's advertised power?
Enter the lower practical limit of the station output and the power your vehicle can accept for a more useful baseline.
How long does a 75 kWh battery take to charge from 20% to 80% at 11 kW?
About 4 hours and 5 minutes in the ideal estimate. Going from 20% to 80% adds 45 kWh, and 45 kWh divided by 11 kW is just over 4 hours. Real sessions often take a little longer.
Why must the target be higher than the current charge?
The calculator estimates the charging time still ahead, so it needs a level above the one you have now. Enter, for example, 20% now and 80% as the goal; both must stay between 0 and 100 percent.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/final3/ev-charging-time-estimate \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"capacity_kwh":75,"current_pct":20,"target_pct":80,"charger_power_kw":11}'const res = await fetch("https://api.kit.forhosting.com/final3/ev-charging-time-estimate", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"capacity_kwh": 75,
"current_pct": 20,
"target_pct": 80,
"charger_power_kw": 11
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/final3/ev-charging-time-estimate",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"capacity_kwh": 75,
"current_pct": 20,
"target_pct": 80,
"charger_power_kw": 11
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/final3/ev-charging-time-estimate", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"capacity_kwh":75,"current_pct":20,"target_pct":80,"charger_power_kw":11}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"capacity_kwh":75,"current_pct":20,"target_pct":80,"charger_power_kw":11}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/final3/ev-charging-time-estimate", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"capacity_kwh": 75,
"current_pct": 20,
"target_pct": 80,
"charger_power_kw": 11
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "final3.ev_charging_time_estimate",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Enter values that describe the charging session
Numeric strings are accepted by the API, although JSON numbers are clearer for automated use.
Technical questions
What does the calculation cost?
The API price is $0.002 per request, and the calculator can also run free in the browser.
Why must the target percentage exceed the current percentage?
The capability estimates time remaining for charging. An equal or lower target represents no charging interval or a discharge calculation, so it returns invalid_input.