# EV Charging Time Calculator

> Estimates how long an electric vehicle takes to charge between two states of charge from its battery capacity, the charger power (capped by the onboard charger for AC charging) and the charging efficiency, plus the energy drawn from the grid and its cost.

- Calculator id: `ev-charging-time` · Category: Home Energy & Electrical (`energy`) · Tool name: `estimate_ev_charging_time`
- Canonical page: https://tttkmbb.com/energy/ev-charging-time · This document: https://tttkmbb.com/energy/ev-charging-time.md · JSON definition: https://tttkmbb.com/energy/ev-charging-time.json

## Purpose

Estimates how long an electric vehicle takes to charge between two states of charge from its battery capacity, the charger power (capped by the onboard charger for AC charging) and the charging efficiency, plus the energy drawn from the grid and its cost.

**Use when:** You want to know how long an EV needs on a home wallbox, a public AC post or a DC fast charger to reach a target charge, or what the session costs at a given electricity price.

**Do not use when:** You need a battery's charge time from ampere-hours and charger current (use battery-charge-time) or the driving range the added energy gives (use ev-range-efficiency); DC fast charging above about 80 % tapers strongly and takes longer than this constant-power estimate.

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `battery_capacity_kwh` | number | kWh | required | Usable battery capacity in kilowatt-hours (e.g. 40, 60, 75, 100). (> 0, max 1000) |
| `start_percent` | number | % | optional, default 20 | State of charge at the start of the session. (min 0, max 100) |
| `target_percent` | number | % | optional, default 80 | State of charge to reach; must be higher than start_percent. (min 0, max 100) |
| `charger_power_kw` | number | kW | required | Power the charging point delivers: 1.4–2.3 kW household socket (Level 1), 7–22 kW wallbox / AC post (Level 2), 50–350 kW DC fast charger. (> 0, max 1000) |
| `max_onboard_charger_kw` | number | kW | optional | Optional maximum AC charging power of the car's onboard charger (commonly 7.4 or 11 kW); the effective power is the lower of the two. Omit for DC charging. (> 0, max 1000) |
| `charging_efficiency_percent` | number | % | optional, default 90 | Share of grid energy stored in the battery; 85–92 % is typical for AC charging (onboard charger and battery losses). (min 50, max 100) |
| `electricity_price_per_kwh` | number | per kWh | optional | Optional price per kWh in your currency for the cost of the session (grid energy × price). (min 0, max 100) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `energy_added_kwh` | number | kWh | battery_capacity_kwh × (target_percent − start_percent) / 100. |
| `energy_from_grid_kwh` | number | kWh | energy_added_kwh / efficiency (what the meter records). |
| `effective_power_kw` | number | kW | min(charger_power_kw, max_onboard_charger_kw). |
| `charging_time_hours` | number | h | energy_from_grid_kwh / effective_power_kw. |
| `charging_time_text` | string |  | Charging time as hours and minutes, e.g. "7 h 9 min". |
| `cost` | number |  | energy_from_grid_kwh × electricity_price_per_kwh; only when a price is given. |
| `range_note` | string |  | Approximate driving range the added energy gives at an example consumption of 160 Wh/km. |

## Formula

`energy_added_kwh = battery_capacity_kwh × (target_percent − start_percent) / 100; energy_from_grid_kwh = energy_added_kwh / (charging_efficiency_percent / 100); effective_power_kw = min(charger_power_kw, max_onboard_charger_kw); charging_time_hours = energy_from_grid_kwh / effective_power_kw; cost = energy_from_grid_kwh × electricity_price_per_kwh`

Constant-power model. AC charging is limited by the car's onboard charger (U.S. DOE: Level 1 ≈ 1.4 kW, Level 2 up to 19.2 kW); DC fast charging is limited by the car's charge curve and slows sharply above about 80 %, so real DC sessions to 100 % take considerably longer.

## Data Sources

- U.S. DOE Alternative Fuels Data Center – Charging Electric Vehicles at Home — https://afdc.energy.gov/fuels/electricity-charging-home (government, retrieved 2026-09-24)
- Wikipedia – Charging station — https://en.wikipedia.org/wiki/Charging_station (reference, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/ev-charging-time?battery_capacity_kwh=…&charger_power_kw=…`
- `POST https://tttkmbb.com/api/v1/calculate/ev-charging-time` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/ev-charging-time · OpenAPI operationId `estimate_ev_charging_time` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool: `estimate_ev_charging_time` (dedicated) or `run_calculator` with `{"calculator_id": "ev-charging-time", "inputs": {…}}`

## Example

- 75 kWh, 20 → 80 %, 7 kW wallbox, 90 %, 0.30 per kWh: inputs `{"battery_capacity_kwh":75,"start_percent":20,"target_percent":80,"charger_power_kw":7,"charging_efficiency_percent":90,"electricity_price_per_kwh":0.3}` → `{"energy_added_kwh":45,"energy_from_grid_kwh":50,"effective_power_kw":7,"charging_time_hours":7.14,"charging_time_text":"7 h 9 min","cost":15}`
- 60 kWh, 10 → 100 %, 11 kW post, 7.4 kW onboard charger: inputs `{"battery_capacity_kwh":60,"start_percent":10,"target_percent":100,"charger_power_kw":11,"max_onboard_charger_kw":7.4}` → `{"energy_added_kwh":54,"energy_from_grid_kwh":60,"effective_power_kw":7.4,"charging_time_hours":8.11,"charging_time_text":"8 h 6 min"}`

```
GET https://tttkmbb.com/api/v1/calculate/ev-charging-time?battery_capacity_kwh=75&start_percent=20&target_percent=80&charger_power_kw=7&charging_efficiency_percent=90&electricity_price_per_kwh=0.3
```

## Limitations

You need a battery's charge time from ampere-hours and charger current (use battery-charge-time) or the driving range the added energy gives (use ev-range-efficiency); DC fast charging above about 80 % tapers strongly and takes longer than this constant-power estimate. Constant-power model. AC charging is limited by the car's onboard charger (U.S. DOE: Level 1 ≈ 1.4 kW, Level 2 up to 19.2 kW); DC fast charging is limited by the car's charge curve and slows sharply above about 80 %, so real DC sessions to 100 % take considerably longer. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Why is my car charging slower than the wallbox rating?**

The onboard charger caps AC power (many cars accept 7.4 kW single-phase or 11 kW three-phase), and cold or nearly full batteries reduce the rate further. Enter the onboard limit in max_onboard_charger_kw.

**Does the efficiency change the cost?**

Yes. The meter records grid energy, which is the battery energy divided by the efficiency, so a 90 % efficient session costs about 11 % more than the energy stored.

**How long does DC fast charging take?**

The estimate holds for 10–80 %; above 80 % chargers taper to protect the battery, and the last 20 % can take as long as the first 70 %.

## Related

- [EV Range and Efficiency Calculator](https://tttkmbb.com/energy/ev-range-efficiency.md) — Range the added energy gives at the car's consumption.
- [Battery Charge Time Calculator](https://tttkmbb.com/engineering/battery-charge-time.md) — Charge time from ampere-hours and charger current.
- [Electricity Cost Calculator](https://tttkmbb.com/everyday/electricity-cost.md) — Cost of the same kWh at several tariffs.