To set a Google Ads budget for a micro SaaS, start from the most you are willing to lose in a month, divide it by 30.4, and use that as your average daily budget. Google can spend up to twice that on a single day, but over a month it keeps charges to about 30.4 times the daily figure. Run a small Search campaign on high-intent keywords for 30 days, track sign-ups and payments, and stop at a loss limit you set before you start.

How Google Ads daily budgets actually work

The daily budget in Google Ads is an average, not a hard daily limit. As of October 2026, Google’s help page on overdelivery and your average daily budget says:

On any one day, a campaign might spend up to twice your average daily budget, to catch days with more traffic.
Across a month, Google aims to charge no more than 30.4 times your average daily budget.

So a $10 daily budget can spend up to $20 on a busy day, and up to about $304 in a month. That is fine if you planned for it. It is a nasty surprise if you thought $10 meant $10.

Two practical results follow:

Plan for the monthly figure, not the daily one. The monthly figure is your real exposure.
Expect uneven days. A $20 day is normal behavior, not a bug. Judge the campaign over weeks.

A real hard cap: the campaign total budget

If you want a fixed ceiling instead of an average, Google offers a campaign total budget for campaigns with set start and end dates. Google’s help page on campaign total budgets says, as of October 2026:

It is available for Search campaigns, among other types.
For Search, Google recommends a run of at least 3 days, and the longest run is 90 days.
You are billed only up to the amount you entered, even if Google serves more traffic than that.
Google tries to spend the total evenly over the run, with no daily limit, so one day can go well past an even share if earlier days spent little.

For a first test, a total budget on a 30-day Search campaign is the simplest way to make your loss limit the actual ceiling. The daily method below still works for campaigns that run with no end date.

Set your Google Ads budget from the monthly cap backward

Work backward from money you can afford to lose while you learn:

Pick your monthly loss limit. The amount you would be fine spending with zero paying customers to show for it. Write it down.
Divide by 30.4. That is your average daily budget.
Round down. A little under the limit is better than a little over.

For example, with a $300 monthly limit: $300 ÷ 30.4 ≈ $9.87. Round down to $9.85. Google’s own ceiling for the month is then about $299, and a single day can reach about $19.70.

If you run several campaigns, each one has its own daily budget. Add up the monthly figures of all of them, and keep the total under your limit.

Google Ads for SaaS: a small test that teaches you something

With a small budget, every click has to count. Set up the test to learn fast.

Campaign type: Search only. People typing a problem or a product type into Google are the closest thing to buyers you can reach with ads. Keep the first test on Search.

Check the networks setting. Google’s help page says that when you create a Search campaign, search partners are included by default. You can turn them off in the campaign settings. Starting with Google Search alone makes the first results easier to read.

Keywords: high intent, few of them.

The job your product does: “invoice reminder software”.
Alternatives to a known tool in your category: “[competitor] alternative”.
A specific pain: “automatic late payment reminders”.

Start with 10 to 20 keywords in phrase or exact match. Broad terms like “invoicing” tend to pull in researchers and students, not buyers.

Negative keywords from day one. Google’s negative keywords keep your ads off searches you don’t want. Typical ones for a SaaS: free, jobs, salary, login, course, tutorial, template. Check the search terms report every few days and add more.

One landing page that matches the ad. If the ad says “late payment reminders”, the page should say it in the headline. Send all test traffic to one page so you can judge it.

Track what matters. Set up conversions for sign-up and, if you can, for payment. Clicks and impressions are not results.

When to stop: write the rule before you start

Running ads before the product converts is on the “did not work” list in the founder threads we read. Protect yourself with rules decided in advance:

A loss limit: your monthly cap from above. When it is spent, the test is over, whatever the dashboard says.
A cost per paying customer you can afford: for example, no more than what a customer pays you in their first three months. That figure is yours to set from your own pricing.
A stop rule: if you have spent two to three times that figure and have no paying customers from ads, pause and fix the page or the offer before spending more.
A weekly check: look at spend, search terms, sign-ups and payments on the same day each week. Put it on your calendar.

If a test works, raise the budget slowly, for example by a fifth at a time, and redo the monthly math after each change.

A 30-day test plan

Days 1 to 3: set the budget from your monthly limit, build one Search campaign with 10 to 20 keywords and your negative list, and test the sign-up conversion yourself.
Days 4 to 14: check search terms every few days, add negatives, and pause keywords that spend without sign-ups.
Days 15 to 30: keep only the keywords that brought sign-ups, and watch for the first payments.
Day 30: compare cost per paying customer with the figure you set at the start. Keep, fix or stop.

When not to run ads yet

Nobody has paid for the product yet. Find your first customers by hand first.
Your landing page converts poorly from free traffic. Ads will not fix it.
You can’t see which sign-ups came from ads. Fix tracking before you spend.

Until then, the free channels in how to promote an app with no audience are a better use of the money. If you run several products, give each its own budget and cap, as in SaaS marketing strategy for several products.

Where Tamarind fits

Tamarind keeps ads under a hard spend cap you set. Every ad change, from a new keyword to a budget edit, waits for your approval unless you put routine ones on autopilot.

Tamarind is in early access. Join the early list to hear when it opens.

Google Ads budget for micro SaaS, with a hard cap