Mid-month budget adjustment calculator

Subtract what has been spent from the monthly budget and divide the rest by the days left, today included. The result is the daily budget that lands the month on target from today.

The formula

budget left       = monthly budget - spend to the end of yesterday
days left         = days in month - today's date + 1
new daily budget  = budget left / days left

A client on €3,000 for a 30-day month has spent €1,700 by the end of the 12th. On the 13th there are 18 days left, today included, and €1,300 to spend: €72.22 a day. The month started on €98.68 a day (€3,000 / 30.4), so the budget comes down by 26.8 per cent.

Why the rest of the month divides by real days

The starting daily budget divides by 30.4, the average month, because that makes Google's monthly ceiling equal the agreed figure. Once the month is under way the question changes. What matters is how many actual days are left to spend the remainder, so the calculator divides by those.

Spend to the end of yesterday is used, not spend so far today. Today's figure is still moving, and both platforms revise recent numbers after the fact, so a completed day is the firmest base to correct from.

What Google may do with the new figure

A lower daily budget does not stop a single expensive day. Google documents that a day can run to twice the average daily budget:

Your daily spending limit (two times your average daily budget for most campaigns) on any particular day.

Source: Google Ads Help, answer 6385083, checked 3 September 2026.

At €72.22 that is up to €144.44 on one day. The adjustment corrects the average; it is not a hard stop. Re-run the numbers a few days after changing a budget, and again in the last week, when a single heavy day moves the month the most.

When the budget is already spent

If spend to date meets or passes the monthly budget, there is no daily figure that puts the month back on target. The choice is to pause, or to agree the overspend with the client before the invoice does it for you. Catching an overspend before your client does covers how to see it coming.

Before the month goes wrong

The Google Ads daily budget calculator sets the starting figure, and the budget pacing calculator tells you whether a client is ahead or behind. Adswave runs the pacing check for every client across Google Ads and Meta and alerts you when one drifts. It is read-only: it tells you the new figure is needed, and you set it in Google or Meta yourself. See overspend alerts or pricing.