Your Seiko kept good time for months, and now it gains five minutes a day. Before you book a service, check the cheap and common cause first: magnetism. Here is how to tell why your Seiko is running fast and how to fix it at home.
First, how fast is “fast”?
| Movement | Seiko’s rated accuracy | Used in |
|---|---|---|
| 4R36 / 4R35 | +45 to -35 seconds a day | Seiko 5 Sports, Turtle, Presage |
| 6R35 | +25 to -15 seconds a day | Mid-range Prospex and Presage |
| 7S26 | No official figure published | SKX007, older Seiko 5 |
If your watch is inside its range, it is working as designed. If it gains minutes a day, read on.
Cause 1: it is magnetized (most likely)
Close to a magnet, the coils of the hairspring can stick together. The spring acts shorter and the watch speeds up. WatchScanning says a magnetized watch typically gains 2 to 10 minutes a day, often starting overnight, and sometimes gains hours or stops.
Common culprits: MagSafe phones and cases, laptop lids, speakers, headphones, magnetic bag clasps, magnetic phone mounts and induction hobs.
The 30-second compass test
- Lay a compass (or a compass app) flat on the table.
- Hold the watch 1 to 2 cm away and move it slowly around the compass.
- If the needle twitches or follows the watch, it is magnetized.
How to demagnetize a watch at home
A small coil demagnetizer costs about $10 to $20. The method matters:
- Hold the button down before the watch touches the coil.
- Put the watch flat on the coil, then slowly lift it away to about 30 cm, still holding the button.
- Release the button only when the watch is far away.
- Repeat the compass test. Do it once or twice more if needed. The case stays closed the whole time.
Do not just tap the button with the watch sitting on the coil. WatchScanning warns this can leave it more magnetized than before.
Cause 2: it is not fully wound
Seiko’s own manual says a 4R-series watch used without being fully wound may gain or lose time, and recommends wearing it more than 10 hours a day. If you only wear it on weekends, see why your Seiko automatic stops.
Cause 3: it needs regulating or a service
If the compass shows nothing and the watch still runs fast, it may simply need regulating, or the oils may have dried. A watchmaker can tell in a minute on a timegrapher. You can measure it yourself first with our guide to checking watch accuracy at home.
Quick fix table
| Symptom | Most likely cause | Fix |
|---|---|---|
| Suddenly gains minutes a day | Magnetism | Compass test, then demagnetize |
| Gains or loses a little more on lazy days | Low wind | Wear it longer or wind it fully |
| Steady error, no magnetism | Needs regulation | Watchmaker regulation |
| Erratic, low power, stops | Needs service | Full service |
Vintage owners: a magnetized 6309 or 7002 behaves the same way. Check its specs in our vintage Seiko reference guides.
Frequently asked questions
How fast is too fast for a Seiko automatic?
Seiko rates the 4R36 at +45 to -35 seconds a day and the 6R35 at +25 to -15. A few seconds a day is normal. Minutes a day means something is wrong, most often magnetism.
Can a phone magnetize my watch?
Yes. WatchScanning names MagSafe phones and cases as the most common cause, followed by laptop lids, speakers, headphones and magnetic bag clasps.
Will magnetism damage my watch?
Rarely. It upsets timekeeping, but demagnetizing usually brings the watch straight back to normal.
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