Why your Google Ads daily spend can exceed your daily budget

A real incident: two days at 175% of budget

A B2B search campaign with a $200 daily budget spent $250.13 on June 9 and $350.68 on June 10. No alerts, no errors, and the Google Ads console reporting everything as normal — because it was.

First check: did the budget itself change?

The obvious suspicion: a tool or teammate bumped the budget. Ruled out. Live budget $200/day, standard delivery, matching config, unchanged since June 3. That would have been the only actual problem; everything below is Google working as designed.

Your “daily” budget is a monthly average

Google’s own name for the setting is average daily budget, and the “average” carries most of the meaning: the budget is a monthly allowance, spent harder on high-demand days and lighter on quiet ones. Only two limits are enforced:

Daily: 2× your average daily budget. The $200/day campaign above may spend up to $400 in a day, so $250.13 and $350.68 were both working as documented.

Monthly: 30.4× your average daily budget (365 days ÷ 12 months). For this campaign that's $6,080, and month-to-date spend was only $1,360, partly because June 1–8 had underspent badly, between $5 and $140 a day. Google's pacing treats every underspent day as room to catch up.

What actually triggered it: a bid ceiling, not the budget

Overdelivery is the permission — something still has to push spend into that band. This campaign bids with Maximize Clicks plus a manual CPC ceiling, and the change history told the story: the ceiling was raised from $3 to $5 on June 2, then $5 to $10 on June 8.

The morning after the second raise, average CPCs jumped from ~$4.90 to ~$9.70, nearly every click pinned right under the new ceiling. Maximize Clicks spends as aggressively as the ceiling allows: double the ceiling, double the CPCs, and the same auction volume lands daily spend in the $200–$400 overdelivery band.

The takeaway: a bid-ceiling raise is a spend change, even though it doesn't touch the budget field. The 2× allowance means the budget won't stop it the same day. If a campaign “suddenly” starts overdelivering, check what was loosened the day before.

If Google overshoots, you get the money back

Served costs (the ads Google showed) can exceed the limits; billed costs can't. When delivery runs past the monthly limit, Google applies an overdelivery credit automatically. In the words of Google's own spending limits documentation, “you’ll never pay more than these two limits.”

Budget changes mid-month reset the math

That $200 budget had been $100 until June 3. After a mid-month change, the monthly limit isn't new budget × 30.4: the rest of the month paces to new budget × remaining calendar days, stacked on top of what was already spent. This campaign's June ceiling is therefore the first two days' spend plus $200 × 28, about $5,700. Ping-ponging a budget mid-month produces spend that no single setting explains.

The exception: pay-for-conversions campaigns

Campaigns billed per conversion rather than per click have no daily spending limit at all; only the monthly 30.4× limit applies. Expect much bigger daily swings.

How to keep spend predictable

1. Budget from the month down. Set the daily budget to monthly target ÷ 30.4. A $3,000 month means $98.68/day, not $100.
2. Judge pacing by the month. A 2× day inside an on-pace month is noise; a month tracking 20% hot is signal.
3. Treat bidding changes as spend changes. Raising a ceiling or target gives Google room it will use the same day.
4. Minimize mid-month budget changes. Each one resets the monthly limit.
5. Set guardrails. Account-level monthly spend limits (on invoiced accounts), or automated rules and budget alerts.

How the investigation actually ran

This took minutes instead of an afternoon of console archaeology because the account runs on Adjar: every budget and bid ceiling lives as config in a git repo.

[[campaigns]]
name = "DB Change Mgmt | SEARCH | 2026-Q2"
bid_strategy = "TARGET_SPEND"
daily_budget_usd = 200
max_cpc_ceiling_usd = 10

One prompt to an AI agent (“double check how the campaign went over budget”) compared the live budget against the TOML, pulled the change-event history, and lined the ceiling raises up with the git log. Budget unchanged, spend inside the 2× allowance, triggered by the June 8 ceiling raise. Every claim above has a receipt.