Overdelivery is when Google Ads spends more than a campaign’s average daily budget on a given day. Google allows a campaign to spend up to twice its daily budget on a busy day, but it limits what you are charged across the month and credits you if delivery goes over that limit.
How overdelivery works
A Google Ads daily budget is an average, not a hard cap. Search volume rises and falls through the week, so Google spends more on days with more opportunity and less on quiet days. Two rules keep this in check:
- The daily limit: a campaign can spend up to two times its average daily budget in a single day.
- The monthly charging limit: across a calendar month you are not charged more than the average daily budget multiplied by 30.4, the average number of days in a month.
Take a campaign with a £50 daily budget. On a busy Monday it might spend £95. Across the month, it cannot charge more than £1,520 (£50 × 30.4). If delivery does exceed that limit, Google records an overdelivery credit on your billing. If you change the budget part-way through the month, or pause the campaign for part of it, the limit is worked out from the budgets and days that actually applied.
Campaigns set up with a campaign total budget work differently. You set one amount for a fixed period, such as a two-week sale, and Google aims to spend it over those dates rather than following the daily average rule.
Why it matters
For a small UK business managing cash flow, a day that costs nearly twice the expected amount can look like a mistake. Usually it is the system working as designed: a cold snap for a boiler engineer, a bank holiday weekend for a garden centre or a news story that sends people searching. Overdelivery lets the campaign take those busy days instead of switching off by mid-morning.
It also affects how charges land. With automatic payments, you are billed when spend reaches your billing threshold or 30 days after your last automatic charge, whichever comes first, so a busy week can bring a card charge sooner than expected.
Common mistakes
- Setting the daily budget to the most you could stand losing in one day, rather than dividing the monthly budget by 30.4.
- Changing budgets several times a week, which makes spend harder to predict and harder for bid strategies to learn from.
- Pausing campaigns on a high-spend day in a panic, which often means missing the busiest buying hours.
- Expecting an overdelivery credit when monthly spend stayed under the charging limit. Days over budget are normal and are not credited on their own.
How to act on it
Work out daily budgets from what you are willing to spend per month, then leave them alone long enough to see a full month’s pattern. Use a budget pacing check once or twice a month to see whether spend is on track, rather than reacting to single days.
If the business truly cannot spend more than a fixed sum in a short window, a campaign total budget gives a firmer limit. Once a month, look in the billing section for any overdelivery credits. Setting budgets and keeping spend on track is part of my PPC management service.