Phone Battery Charge Time Calculator
Estimate how long a battery takes to charge from its capacity, charger current and charging efficiency.
How it works
Time = capacity needed ÷ (charger current × efficiency)
Charging is not perfectly efficient — some energy becomes heat — so real time is longer than capacity ÷ current. Fast chargers also slow down near 100% to protect the battery, so the last 20% takes longer than this estimate.
Worked example
A 4,000 mAh battery from 20% on a 2,000 mA charger at 80% efficiency takes about 2 hours.
Frequently asked questions
Why does charging slow near 100%?
Phones taper the current above roughly 80% to reduce heat and extend battery lifespan, so the top end is slower than a linear estimate.
What efficiency should I use?
80–90% is typical for wired charging; wireless charging is lower, often 60–75%.
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This calculator is for educational purposes. Double-check important results before acting on them.