Over seven days, an Acme Watches ad set has 84,000 impressions and 30,000 people reached, a frequency of 84,000 / 30,000 = 2.8. Over 30 days it shows 290,000 impressions and 52,000 people reached, a frequency of 5.6, because most of the extra impressions went to people it had already reached.

Some repetition helps, since people rarely buy on the first view. Too much means paying to remind people who have already decided. Frequency alone does not tell you when you have crossed that line. A common starting point is frequency above 3 alongside a CTR drop of about 20%, but that is a rule of thumb that varies by account, product and audience size.

Read frequency over a fixed window, since it only grows as the window gets longer. If it climbs while results fall, widen the audience, add fresh creative or move budget to broader prospecting. Accept higher frequency in retargeting, where the audience is small by design.