Why a watch needs servicing at all
A mechanical movement is a machine running continuously — a balance oscillating millions of times a week — lubricated by microscopic quantities of oil on its bearings and contact surfaces. Over years, those oils thin, migrate, and dry; metal then runs on metal, wear accelerates, and timekeeping drifts. A service is a full rebuild that restores the lubrication before that wear becomes damage. Unlike a car, a watch gives almost no warning: it keeps running well past the point where its oils have failed, which is precisely why service is scheduled by time rather than by symptom.
What actually happens in a service
A proper full service is involved. The watchmaker disassembles the movement completely — every wheel, bridge, and screw — cleans the parts ultrasonically, inspects them under magnification for wear, replaces worn components and all gaskets, reassembles, lubricates each point with the correct oil or grease (there are several, each formulated for a specific load), then regulates the watch across positions and pressure-tests the case. Done correctly it takes hours of skilled labor, which is most of what you are paying for. A cursory "service" that merely oils the movement without full disassembly is not a service; it is a postponement.
The honest answer is "less often than brands suggest, more often than optimists hope." Modern watches with current lubricants commonly go 5 to 10 years between services; many run well beyond their nominal interval. Rather than service on a rigid calendar, watch for signs — a watch losing or gaining noticeably more than before, a drop in power reserve, a chronograph or date acting up, or moisture under the crystal (service immediately). A watch keeping good time and full reserve is usually telling the truth about its health. Water-resistant watches used in water are the exception: test the seals regularly regardless.
Reading the quote
Service pricing spans a wide range, and understanding the drivers prevents both overpaying and false economy. A simple time-and-date automatic runs roughly $300–700 at an independent watchmaker, more at a brand service center. A chronograph costs more — more parts, more complexity — typically $500–1,200. Perpetual calendars, repeaters, and tourbillons run into the thousands, because the labor and expertise scale with the complication. The other major variable is who does the work: brand service centers charge a premium and often replace parts wholesale (sometimes including dials and hands, which can harm a vintage watch's originality), while a skilled independent watchmaker usually costs less, communicates more, and preserves originality if asked. For vintage and collectible watches, a trusted independent who understands originality is frequently the better choice; for modern watches under warranty, the brand center keeps the warranty intact.
Necessary work versus upsell
A trustworthy quote itemizes: cleaning and lubrication, parts to be replaced and why, regulation, and a water-resistance test. Be alert to a few patterns. Mandatory case refinishing — polishing the case as part of "service" — should always be optional and, on vintage or collectible watches, usually declined, since polishing removes metal and erodes value; insist the case be left untouched unless you ask otherwise. Wholesale parts replacement on a watch that does not need it inflates the bill; ask which parts are genuinely worn. And a reputable watchmaker will return your old parts if asked, which both confirms the work was done and matters for originality on collectible pieces. The clearest sign of a good relationship is a watchmaker who explains what the watch needs, what it does not, and why — and who is comfortable being asked.
A service is a scheduled rebuild that renews the lubrication before wear turns into damage — necessary, periodic, and worth doing well rather than cheaply. Learn what the work involves and you can read any quote: pay for full disassembly, correct lubrication, honest parts, and a pressure test; decline the polishing; keep your old parts; and choose the watchmaker — independent or brand — that fits whether the watch is a tool to keep running or an object to keep original.