A slow or fast automatic is usually telling you one of about six things — and several you can diagnose and fix in minutes, for nothing. Here is how to find the cause in the right order, before you spend money on a service you may not need.
Before You Panic
Your automatic watch was keeping near-perfect time, and now it is drifting — a few minutes a week, or something far worse. The instinct is to assume it is broken and book an expensive service, but in most cases a slow or fast automatic is telling you one of roughly six things, and several of them you can diagnose and fix yourself in a few minutes without spending anything. The trick is to work through the possibilities in the right order, from the most common and cheapest to the rarest and most serious, rather than jumping straight to the worst conclusion.
First, What Counts as a Problem?
Mechanical watches are not quartz, and they are not supposed to be. Inside an automatic, a balance wheel oscillates several times every second, and that mechanical timekeeping is allowed to drift within a tolerance. Knowing your watch's tolerance stops you chasing a fault that does not exist. Most non-certified movements — which is to say most watches — are designed to run within roughly minus ten to plus twenty seconds a day. A COSC chronometer-certified movement holds to minus four to plus six seconds a day, and the most accurate movements, such as Rolex's Superlative Chronometer or Omega's Master Chronometer ratings, keep to just a few seconds a day. If your watch is running within its own specification, nothing is wrong with it. A non-chronometer losing eight seconds a day is performing exactly as designed; you will simply lose a minute or so every week and a half, which is the normal price of mechanical charm. The cases worth investigating are when a watch suddenly drifts far outside its spec, or changes its behaviour after years of consistency.
The Most Common Cause: It Isn't Wound Enough
An automatic winds itself from the motion of your wrist, and if it does not get enough motion it never reaches full tension in the mainspring. This is the single most common reason a watch keeps poor time, and it is especially likely if you have a desk-bound, low-movement lifestyle, or if you only wear the watch for part of the day. A partially wound movement runs with reduced amplitude, and low amplitude makes a watch run slow and erratically. The fix costs nothing: hand-wind the watch to full each morning, with the crown in its neutral winding position, turning it clockwise around thirty to forty turns, or simply wear it more consistently. If the accuracy snaps back once the watch is fully wound, you have found your answer, and it was never a fault at all.
The Most Common Sudden Cause: Magnetisation
If the change was sudden — the watch was fine, and then it was wildly off — suspect magnetisation before anything else. Modern life is saturated with magnets, and a magnetised hairspring sticks to itself, which can throw a watch off by many minutes a day. The usual culprits are phone speakers and magnetic phone cases, tablet covers, laptop lids, induction cooktops, magnetic handbag and wallet clasps, and even some headphones. Testing for it is simple: hold a compass next to the watch and slowly rotate the watch, and if the compass needle swings as the watch moves, the watch is magnetised. A magnetometer app on your phone will show the same effect. The fix is one of the cheapest and most satisfying in all of watchmaking. A small bench demagnetiser costs very little, or any watchmaker will demagnetise the watch in about two minutes for a token fee, and a watch that was running minutes off will often return to normal accuracy the instant it is demagnetised. An enormous share of "my watch suddenly went crazy" complaints are nothing more than this.
Positional Variance — and How to Use It
A mechanical watch runs at slightly different rates depending on its orientation, because gravity acts on the balance differently in each position. On the wrist these positions average out over a day, but how you rest the watch overnight can nudge the daily average faster or slower, and you can turn this into a free regulation trick. If your watch runs a touch fast, try resting it dial-up or crown-up overnight; if it runs slow, experiment with crown-down or dial-down. Try a single position for a few nights, measure the result, and adjust. Many owners bring an otherwise healthy watch to near-perfect timekeeping simply by finding its best resting position, no watchmaker required.
How to Actually Measure the Rate
Before you can fix accuracy you have to measure it properly, and "it felt slow" is not a measurement. The simplest reliable method is to set the watch precisely against an authoritative reference — a phone's atomic-synced clock, or a site such as time.is — at a fixed moment, wear it normally, and compare again at exactly the same time twenty-four hours later; the difference is your daily rate. Do this across several days for an average, because any single day can be skewed by how active you were and how the watch rested. For a closer look, free smartphone timegrapher apps use the phone's microphone to listen to the balance and estimate both rate and amplitude; they are not as precise as a real timing machine, but they are useful for spotting a genuine problem. A true mechanical timegrapher, the instrument a watchmaker uses, is the definitive tool if you want certainty.
Amplitude: The Number Behind the Symptom
When watchmakers diagnose timekeeping, they look past the rate to amplitude, which is how far the balance wheel swings on each beat, measured in degrees. Healthy amplitude sits somewhere around 270 to 310 degrees when the watch is fully wound. Low amplitude is the hidden cause behind a great deal of poor timekeeping, and it is exactly what you get from an under-wound watch, degraded lubricants, or a tired mainspring. This is why the earlier fixes work the way they do. Winding the watch fully raises its amplitude, which is why topping up the wind so often restores good timekeeping. A worn-out movement that genuinely needs service shows chronically low amplitude that no amount of winding can lift. So the test is revealing: if fully winding the watch restores its accuracy, amplitude was your issue and the cause is entirely benign, but if a fully wound and demagnetised watch still keeps poor time, low amplitude from wear is the likely story and a service is due.
Temperature, Shock, and Watches That Stop
Two further causes are worth knowing. Extreme cold thickens the lubricants and slows the movement, while extreme heat can speed it up, so a watch that times differently in very different conditions may simply be reacting to temperature. A sharp knock — dropping the watch, or a hard bump against a door frame — can shift the regulator or, in a bad case, damage a pivot, and if the accuracy changed immediately after an impact, that points to a mechanical cause rather than a magnetic one. A related complaint is a watch that stops completely while you are wearing it, which is usually nothing more than insufficient daily motion to keep it wound; give it thirty to forty hand-winds and see whether it then holds. If a fully wound watch still stops on the wrist, or stops after a knock, that suggests a mechanical fault and a trip to the watchmaker. And once again, if it stops with moisture visible under the crystal, treat it as urgent, because water inside the case is the one symptom you should never wait on.
A Simple Diagnostic Order
Putting it together, a sensible sequence keeps this cheap and clear. Confirm the watch is fully wound, then measure its daily rate over a full twenty-four hours. Check that rate against the watch's specification, and if it falls within spec, stop, because nothing is wrong. If it is out of spec, test for magnetisation with a compass and demagnetise if needed, which resolves a remarkable number of cases on its own. Next, experiment with the overnight resting position to use positional variance in your favour. Only when the watch is well-powered, demagnetised, undamaged, and still drifting far outside its specification should you conclude that the movement needs a professional service. Most "my automatic is losing time" cases never get past winding or demagnetising, and knowing the difference saves you both money and a needless month without your watch.
Frequently Asked Questions
Why is my automatic watch suddenly losing time?
The most common cause of a sudden change is magnetisation from exposure to phone speakers, laptop lids, magnetic clasps and similar magnets. Test it by holding a compass next to the watch and rotating it; if the needle moves, it is magnetised. Demagnetising is cheap, takes about two minutes, and usually restores normal accuracy immediately.
How many seconds a day is acceptable for an automatic watch?
Most non-certified movements are designed to run within roughly minus ten to plus twenty seconds per day. COSC chronometer-certified watches run within minus four to plus six seconds per day, and the most accurate movements hold to just a few seconds a day. If your watch is within its specification, it is performing normally.
Can I fix a watch that loses time myself?
Often yes. Make sure it is fully wound, test for and remove any magnetisation, and experiment with the overnight resting position to use positional variance in your favour. These steps resolve the majority of cases. Only a watch that is well-powered, demagnetised, undamaged and still far out of spec is likely to need a professional service.
Does how I store my watch overnight affect its accuracy?
Yes. A mechanical watch runs at slightly different rates depending on its orientation, because gravity affects the balance. If your watch runs fast, try resting it dial-up or crown-up; if it runs slow, try crown-down or dial-down. Many owners fine-tune their timekeeping to near-perfect simply by choosing the right resting position.
Why does my automatic watch lose time when I don't wear it much?
If you do not wear it enough, the mainspring never fully winds, and a partially wound movement runs with low amplitude, which makes it slow and erratic. Hand-winding it to full or wearing it more consistently usually fixes this, and a watch winder can help if you rotate between several watches.
Is it bad if my watch gains time instead of losing it?
Not necessarily. Running slightly fast is within spec for many watches and is often preferred because it is easy to reset. But a watch that suddenly gains many minutes a day is most likely magnetised — the same cheap, fixable cause as one that suddenly loses time.
A Note on This Guide
This guide is provided for general informational purposes and describes common, non-invasive checks any owner can perform. It is not a substitute for professional diagnosis. Demagnetising tools and timegrapher apps are widely available, but if you are unsure, or the watch is valuable, take it to a qualified watchmaker rather than attempting internal adjustments yourself. Never open the caseback to investigate timekeeping unless you are trained to do so.