An overhaul is a maintenance service that a watch needs at regular intervals.

In a mechanical watch, oils and greases deteriorate after a few years. Whether the watch works or not, the lubrication will have to be renewed at some point. On an automatic watch it is sometimes the pawl wheels that do not work efficiently anymore and the watch does not wind up correctly. Sometimes also the precision is not good anymore. Also with the years the gaskets can dry out and a waterproof watch can become leaky. Thus the watch will have to be revised.

As a rule, a mechanical watch needs to be serviced every five years or so. This also prevents parts where the lubrication is no longer effective enough from wearing out. An overhaul can be considered more tedious than assembling the same watch when it was first assembled. Indeed, a large part of the movement will have to be disassembled and the parts cleaned. When reassembling, each part will be checked. On a modern watch the worn parts will sometimes be replaced. On an old watch they will be repolished when necessary because standard parts for exchange do not exist sometimes.

Once the overhaul is completed, a mechanical watch can be observed for a good week or more. If it is automatic, the efficiency of the automatic system will often be checked. Also the running will sometimes be checked on a simulator. The whole process of an overhaul will therefore consist of disassembly, cleaning, assembly and lubrication, and finally controls.

On a quartz watch the process will be a little simpler. Often it will consist mainly of a change of battery and gasket and a water-resistance check. Indeed, in a quartz mechanism a gear is not under the constant tension of a spring as in a mechanical watch. Thus its gearing is often not lubricated. This makes the task easier during the revisions of quartz watches.