A charge already added to your bill can mean several different things, and the difference matters. Sometimes it's a legally mandated charge that genuinely covers staff wages (Switzerland, France). Sometimes it's a mandatory charge that may or may not reach the person who served you (Dubai, some US venues). Sometimes it's technically discretionary even though it's printed on the bill (the UK). And sometimes it's added specifically because a venue is in a tourist-heavy area, in a way locals wouldn't normally see.
There's no single percentage here — the point of this page is to help you read the bill itself rather than guess. Look for the exact wording: “service charge”, “service compris”, “gratuity”, “admin fee” and “cover charge” are not interchangeable, and each carries different rules about whether staff actually receive it.
If in doubt: check whether the charge is described as included in your destination's country or city guide on this site, ask directly whether the listed charge goes to staff, and if you want to be certain your money reaches the person who served you, a small cash tip handed over directly is the most reliable method almost everywhere.
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