Wondering how long your phone, laptop or power bank will take to charge? Enter the battery size, charger power and charge levels, and this free calculator gives a realistic estimate, including the slower final stretch near 100 percent.
Charging Time Calculator
Estimate how long a phone, laptop or power bank takes to charge with your charger.
Charging time FAQ
How do I calculate charging time?
Convert the battery to watt-hours, multiply by the percentage you need to add, and divide by the effective charging power, which is the charger watts times the efficiency. Add extra time for the slower final stretch.
Why does charging slow down after 80 percent?
Lithium batteries reduce charging current as they fill up to avoid heat and wear. That is why the last 20 percent often takes as long as the first 50 to 60 percent.
Will a more powerful charger always charge faster?
No. Your device only accepts up to its own maximum charging power. A 100 W charger will not speed up a phone that tops out at 25 W, but it is safe to use because the device controls how much it draws.
Does the cable matter?
Yes. A poor or low-rated cable can limit current and slow charging. For higher wattages, use a cable rated for the power level, such as a 5 A USB-C cable for fast laptop charging.
How the estimate is calculated
The calculator converts the battery to watt-hours, works out how much energy you need to add, and divides by the effective charging power (charger watts × efficiency). If your device limits its maximum charging power, that limit is used instead. Above 80 percent, charging is assumed to run about 2.5 times slower, which matches how lithium batteries behave.
What affects real charging time
- Device limit: a phone that accepts 25 W will not charge faster on a 65 W charger.
- Cable quality: low-rated cables can restrict current.
- Heat: warm batteries charge more slowly to protect themselves.
- Usage: gaming or video while charging takes power away from the battery.
Tips for faster and healthier charging
- Use the charger and cable that came with your device, or ones that support the same fast-charging standard.
- Charge in a cool place and remove thick cases if the phone gets warm.
- Keeping a battery between about 20 and 80 percent when you can is gentler on its long-term health.