Battery Charge Time Calculator
Enter your battery capacity, charger output current, current battery level and charging efficiency to see exactly how long a full charge will take — in hours and minutes.
mAh
mA
%
%
2 h 13 min from 20% to 100%
- 1
Charge needed
5,000 mAh × (1 − 20% ÷ 100) = 4,000 mAh - 2
Effective charge current
2,000 mA × 90% ÷ 100 = 1,800 mACharging efficiency accounts for heat losses in the cable and circuit. - 3
Charge time
4,000 ÷ 1,800 = 2.22
How does this calculator work?
Charge time (hours) = capacity (mAh) × (1 − start%) ÷ (charger mA × efficiency). A 5 000 mAh battery from 20% to 100% on a 2 000 mA charger at 90% efficiency takes about 2.2 hours. The last 20% (constant-voltage phase) may take longer than this constant-current estimate suggests.
Formula
How this is calculated
In the simplest model, charge time equals the amount of charge remaining (mAh) divided by the charger's current output (mA), giving hours. A 5 000 mAh battery charged at 1 000 mA takes about 5 hours from flat. In practice, charging is not 100% efficient — a portion of the electrical energy is lost as heat in the cable, charging circuit and battery itself. Li-ion chargers typically run at 85–95% efficiency; the efficiency drops at very high currents (fast charging) and at very high or very low temperatures.
The C-rate is a shorthand for charging speed: 1C means the charger delivers enough current to theoretically fill the battery in one hour (e.g. 5 000 mA for a 5 000 mAh battery). 0.5C takes two hours; 2C theoretically takes 30 minutes but manufacturers typically limit fast-charge to the first 80% of capacity to protect battery health.
This calculator uses a constant-current model, which is accurate for the bulk-charge phase (roughly 0–80%). Modern chargers then switch to a slower constant-voltage phase for the last 20%, so real times from 80 to 100% may be longer than the estimate — the formula gives a useful lower bound.
Frequently asked questions
Look at the label on the charger's plug or the output section of its spec sticker — it will say something like "Output: 5V ⎓ 2A" or "5V / 2000mA". The ampere (A) figure × 1000 = milliamperes (mA). For USB-C PD chargers the wattage varies by voltage profile; at 5V a 20W charger delivers 4A (4000mA).
Li-ion batteries are charged in two phases: a fast constant-current (CC) phase from 0 to ~80%, followed by a slower constant-voltage (CV) phase from 80 to 100%, where current tapers off to protect the battery. This calculator models only the CC phase, so actual 80→100% time may be 30–60% longer than the proportional estimate.
High charge rates (2C and above) generate more heat and can accelerate lithium plating, both of which gradually reduce battery lifespan. Most smartphones use adaptive charging that slows at night or above 80% to mitigate this. For longevity, keeping charge between 20–80% and avoiding sustained fast-charging at high temperatures is recommended.
TG we-Calculate Editorial Team. (2026). Battery Charge Time Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/battery-charge-time-calculator
TG we-Calculate Editorial Team. "Battery Charge Time Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/battery-charge-time-calculator.
TG we-Calculate Editorial Team, "Battery Charge Time Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/battery-charge-time-calculator
@misc{wecalculate_battery_charge_time_calculator, title = {Battery Charge Time Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/battery-charge-time-calculator}}, year = {2026}, note = {TG we-Calculate} }
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