How fast does 20W charge an iPhone?
The short answer
With a 20W USB-C charger, most iPhones from iPhone 12 onward draw about 18–19.5W at first. They reach roughly 50% in 27–35 minutes, then slow down on purpose. Independent tests measured 50% in 32 minutes and full in 2 hours 11 minutes on an iPhone 14 Plus 1, and 50% in 27 minutes and full in 1 hour 50 minutes on an iPhone 17. 2 Heat, Optimized Battery Charging, a Charge Limit or the wrong cable can make it slower.
In 30 seconds
- Fast first, gentle later. The first half charges quickly; the last 20% takes longest. That is by design. 34
- Typical 20W timings: about 50% in half an hour, full in about 1 hour 50 minutes to 2 hours 20 minutes, depending on model. 152
- Slow? Check five things: temperature, Charge Limit or Optimized Battery Charging, the cable, what the phone is doing, and whether the charger is really delivering USB Power Delivery.
How an iPhone charges: the shape of the curve
Lithium-ion batteries charge in two phases. In the first, constant current, the charger pushes a steady, high current and the battery voltage rises. In the second, constant voltage, the voltage is held at its maximum and the current tapers away as the battery fills. Charging ends when the current falls to a small fraction of the battery's capacity. 6
Apple describes this as fast charging "to quickly reach 80% of its capacity", then switching to slower trickle charging. 4 So the clock does not run evenly. The first 50% can take under half an hour; the last 20% can take nearly as long as the first 50%.
- 19.5 W · until about 37 min
- 15 W
- 8.5 W
Show the numbers
| Phase | Approximate power (W) | Until (min) |
|---|---|---|
| 1 | 19.5 | 37 |
| 2 | 15 | Not timed by the source |
| 3 | 8.5 | Not timed by the source |
- iPhone 14 Plus · Apple A2940
Show the numbers
| Series | Battery (%) | Time (min) |
|---|---|---|
| iPhone 14 Plus · Apple A2940 | 50 | 32 |
| iPhone 14 Plus · Apple A2940 | 80 | 60 |
| iPhone 14 Plus · Apple A2940 | 100 | 131 |
- iPhone 17 · 20W
Show the numbers
| Series | Battery (%) | Time (min) |
|---|---|---|
| iPhone 17 · 20W | 50 | 27 |
| iPhone 17 · 20W | 80 | 52 |
| iPhone 17 · 20W | 100 | 110 |
Typical 20W timings by model (independent tests)
| iPhone | 50% | 80% | 100% | Source |
|---|---|---|---|---|
| iPhone 12 | 57% at 30 min | — | — | Tom's Guide, Oct 2020 7 |
| iPhone 14 Plus | 32 min | 60 min | 2 h 11 min | ChargerLAB, Sep 2023 1 |
| iPhone 15 Pro Max | — | — | 2 h 21 min | 9to5Mac, Oct 2023 5 |
| iPhone 16 Pro | — | — | 2 h 6 min | ChargerLAB, 25 °C, Dec 2024 8 |
| iPhone 17 | 27 min | 52 min | 1 h 50 min | ChargerLAB via Notebookcheck, 25 °C, Nov 2025 2 |
Each test used one phone, one adapter and one starting condition. Your results will vary with temperature, battery age and use during charging.
Apple's own figures, and why they differ
Apple's India store page for its 20W adapter says: up to 50% in "around 35 minutes" with iPhone 8 or later. 9 Apple's support page gives "around 30 minutes" for iPhone 17e and iPhone Air with a 20W adapter or higher. 10 The figures come from Apple's testing of drained units, timed from when the Apple logo appears, and Apple notes that results vary. 1110 Both are reasonable expectations. Quote the one that matches your model.
Why your iPhone may charge more slowly
1. It is too warm (or too cold)
Apple says fast charging may not work when conditions are too hot or too cold. 10 It also says software may limit charging above 80% when recommended battery temperatures are exceeded. 4 In an Indian summer, a phone charging in a hot car, in direct sun or under a pillow will slow down to protect its battery. Move it somewhere cooler and take it out of a thick case.
2. Optimized Battery Charging or a Charge Limit is on
On iPhone 15 and later, you can set a Charge Limit between 80% and 100% in 5% steps. The iPhone charges to within a few percent of it and stops. 3 Optimized Battery Charging learns your routine and may hold the charge at 80% until shortly before you usually unplug. 3 Both are working as intended. Check them in Settings › Battery › Charging.
3. The cable
- iPhone 15 and later (USB-C): any USB-C to USB-C cable that meets the USB specification carries 20W. At 3 A or less, an electronically marked (e-marked) cable is not needed. 12
- iPhone 14 and earlier (Lightning): fast charging needs a USB-C to Lightning cable. Apple's requirement lists USB-C adapters with a USB-C to Lightning cable for earlier models. 10 Uncertified Lightning cables may charge slowly or stop working.
- A frayed or loose cable, or lint in the port, can also cut charging.
4. What the iPhone is doing
Gaming, navigation, video calls or a bright screen use power while you charge, so the battery fills more slowly. Some independent testers measured iPhones drawing about 10 W from a 20W adapter in some conditions. 1
5. The charger is not delivering USB Power Delivery
If a charger falls back to basic 5 V USB, the iPhone may charge at a fraction of 20W. Possible causes: a counterfeit or non-compliant adapter, a USB-A port, or an adapter-to-adapter chain. A USB-C power meter, a small inline tester, will show whether the charger is at 9 V while the iPhone fast charges.
The "Slow Charger" message
Recent iOS versions can show "Slow Charger" on the battery screen. 13 It indicates the iPhone thinks it is drawing less power than it could. Apple has not published the exact wattage threshold that triggers it, and we do not guess it. Work through the checklist below. If the message persists with a USB PD charger of the right rating, a known-good cable and a cool phone, try another wall socket and contact the charger's maker.
Troubleshooter: my iPhone charges slowly on 20W
- Is the phone hot to the touch, or in a hot place? → Yes: cool it, remove the case, retry. → No: go to 2.
- Is the battery already above 80%? → Yes: slower charging is normal; check Charge Limit and Optimized Battery Charging. → No: go to 3.
- iPhone 14 or earlier: are you using a USB-C to Lightning cable? → No: you need one for fast charging. → Yes, or iPhone 15 and later: go to 4.
- Does a different, known-good cable help? → Yes: replace the cable. → No: go to 5.
- Is the phone busy (game, navigation, hotspot)? → Yes: pause it and retry. → No: go to 6.
- Does a USB-C meter show about 9 V during charging? → No, 5 V only: the adapter is not negotiating USB Power Delivery; try another adapter and check the first one's authenticity and BIS registration. → Yes: go to 7.
- Still slow? Clean the port gently, try another socket, restart the iPhone. If it persists, contact Apple support for the phone or the charger's maker.
Heat: what is normal for the charger
Chargers get warm. In ChargerLAB's test, Apple's 20W adapter reached 42.1 °C on the front and 49.5 °C on the back after an hour at full 20W, at 220 V input in a 25 °C room. 1 Warm is normal. Too hot to hold, a burning smell, discolouration, or heat with nothing connected are reasons to unplug and stop using it. More in efficiency and heat.
Myths
"Leaving it on the charger overnight overcharges the battery." iPhone stops charging when full, and Optimized Battery Charging may hold at 80% overnight. 3
"If it stops at 80%, the charger is faulty." Usually it is Optimized Battery Charging, a Charge Limit or temperature management. 34
"A 20W charger is too slow for modern iPhones." For iPhone 16 and earlier, Air and 17e it meets Apple's requirement. 10 Newer Pro models charge fastest on higher-wattage adapters; see 20W vs 30W.
"Fast charging damages the battery." Battery ageing comes from a combination of factors, especially temperature history and charging pattern. 3 iPhone manages charging speed itself.
Frequently asked questions
How long does a 20W charger take to fully charge an iPhone? About 1 hour 50 minutes to 2 hours 20 minutes in independent tests, depending on model. 1582
Why does my iPhone charge fast to 50% and then slow down? That is the battery moving from constant-current to constant-voltage charging, which iPhone uses to protect the battery. 64
Why does my iPhone stop at 80%? Optimized Battery Charging, a Charge Limit (iPhone 15 and later) or high temperature. 34
Does my iPhone need a special cable for 20W? iPhone 15 and later: a standard USB-C cable. iPhone 14 and earlier: a USB-C to Lightning cable. 10
What does "Slow Charger" mean? That the iPhone believes it could charge faster. Apple has not published the threshold. Check the cable, temperature and charger, using the troubleshooter above. 13
Is it normal for the charger to be warm? Yes. A 20W adapter at full load can reach 40–50 °C on its surface. 1
Comparative caveats
All timings are third-party results on Apple's own adapters, quoted with source, model and conditions. They are expectations for a 20W USB PD charger in general. They are not ERONIX results.