Answer
What counts as good accuracy for a mechanical watch?
Short answer
Within about 5 seconds a day is good for any mechanical watch, and within 10 is perfectly normal. Chronometers are certified to a mean daily rate of minus 4 to plus 6 seconds a day, while ordinary automatics typically run roughly minus 10 to plus 20. A steady rate matters more than a small one, because steady can be regulated.
On this page (5 sections)
Good is within about 5 seconds a day, measured as a seven-day average of normal wear. Normal is within 10. A certified chronometer is tested to a mean daily rate of minus 4 to plus 6 seconds a day, and an ordinary non-certified automatic typically lands somewhere between minus 10 and plus 20.
Those are the headline numbers, but they are only half of the answer. The other half is whether the rate is the same next week, because a repeatable rate can be regulated to near zero in minutes while an erratic one cannot be fixed at any price short of a bench.
The realistic scale
| Mean daily rate | Verdict | Drift over a month |
|---|---|---|
| Within 2 seconds a day | Excellent. Chronometer territory or better | about 1 minute |
| 2 to 5 seconds a day | Good. A well-adjusted, healthy movement | 1 to 2.5 minutes |
| 5 to 10 seconds a day | Normal for a modern automatic | 2.5 to 5 minutes |
| 10 to 20 seconds a day | Acceptable but worth regulating | 5 to 10 minutes |
| Beyond 20 seconds a day | Outside most specifications. Investigate | over 10 minutes |
The right-hand column is the one that decides whether you care. Five seconds a day is roughly 35 seconds a week, so a watch you reset on the first of each month is never more than a couple of minutes out. Fifteen seconds a day means resetting weekly. Neither is a defect; they are different amounts of nuisance.
Good depends on what the movement claims
There is no universal standard for a non-certified watch, so the fair test is the tolerance published for that specific caliber. Budget Japanese automatics are often specified at roughly minus 35 to plus 45 seconds a day, a deliberately wide band that most examples beat comfortably. Standard-grade Swiss automatics are typically specified around plus or minus 12 seconds a day, adjusted in two positions. Upgraded grades tighten that to roughly plus or minus 4 to 7 seconds, adjusted in more positions, and chronometer grades go to the COSC band.
A watch running plus 18 seconds a day is a disappointment on a chronometer and unremarkable on an entry-level automatic. Check the specification before deciding you have a problem, using our guide to reading a watch specification.
Consistency is the real measure
Standards agree with this, which is why COSC uses seven criteria rather than one. Three of them constrain variation rather than rate: a movement averaging plus 1 second a day by lurching between positions fails certification even though its headline figure looks perfect.
At home, the equivalent checks are simple. Does the weekly average hold from week to week within a second or two? Is the day-to-day scatter small, or does it swing wildly with how active you were? And if you run a positional test, how big is the delta between the fastest and slowest position? A tight delta means your rate will not depend on what you did on Tuesday.
What is achievable, and what is not
A mechanical watch is a metal spring driving a metal oscillator through oil, subject to gravity, temperature and magnetic fields. That physics sets the ceiling. A superbly adjusted movement in daily wear settles within a few seconds a day; nothing mechanical reaches quartz territory, where an ordinary movement holds about 15 seconds a month.
So do not chase a number the machine cannot hold. Expect the weekly average to move a second or two between a hot month and a cold one, or between an active week and a desk-bound one. A watch that averaged plus 3 in March and plus 5 in July is not developing a fault. Our guide to accuracy and chronometer standards covers how the certified figures are produced and why they translate imperfectly to a wrist.
When a number stops being good enough
Four patterns are worth acting on, whatever the absolute figure.
- A rate that has changed suddenly. Demagnetize first, then re-measure for a week.
- A rate that is getting steadily worse over months. Usually aging lubricant, and the cue for a service conversation.
- A watch that keeps good time worn but stops when rested. Low amplitude, which is a bench problem rather than an accuracy problem.
- A rate that is fine at full wind and poor by the second day. A torque or mainspring issue.
Otherwise, measure once, decide whether the drift genuinely bothers you, and either have the watch regulated or leave it alone. Seven days of readings and the accuracy calculator will tell you which of those you are dealing with, and our guide to timing your own watch explains how to gather the data properly.
Common follow-up questions
Is plus 15 seconds a day bad?
Not necessarily. It is inside the published tolerance of many budget and standard-grade calibers, and if it is steady week after week it is a regulation job rather than a fault. What would concern a watchmaker is plus 15 one week and minus 5 the next, or plus 15 accompanied by low amplitude.
Should I expect a new watch to be accurate out of the box?
Expect it to be inside the specification printed for that caliber, which may be a wide band. Factory regulation is done on a bench, in a couple of positions, before the movement met your wrist. A watch that is technically in specification but not to your taste is a candidate for regulation, not a warranty claim.
Does a higher beat rate mean better accuracy?
Indirectly, and less than people assume. A 4 Hz balance is disturbed proportionally less by a knock than a 2.5 Hz one and recovers faster, which helps stability. But adjustment, amplitude and condition matter far more, and there are superb low-beat movements and mediocre high-beat ones.
How much accuracy does a vintage watch lose with age?
Age itself is not the problem; service history is. A properly serviced 1960s chronometer can still keep time to a few seconds a day. Expect a wider positional spread and a rate that varies more with temperature than a modern movement, and treat anything worse than roughly 30 seconds a day as a service question.
Sources and further reading
- ISO 3159, Timekeeping instruments: wrist-chronometers with spring balance oscillator, for the mean daily rate and variation criteria.
- Contrôle Officiel Suisse des Chronomètres (COSC), published certification criteria for mechanical wristwatch movements.
- METAS, Master Chronometer certification documentation, for the 0 to plus 5 seconds a day tolerance measured on the cased watch.
- Movement manufacturers' technical data sheets (ETA, Sellita, Seiko, Citizen), which publish rate tolerances by grade and the number of positions adjusted.
- Witschi Electronic, timing machine documentation, for healthy amplitude ranges and the interpretation of positional delta.
Last reviewed 4 September 2026. Spotted an error? Tell us and we will fix it in public.