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Setting a Google Ads budget for SaaS

The right Google Ads budget depends on what you want to do. A budget sized to learn looks different from a budget sized to scale. This article covers three common frameworks, when each applies, and the math.

The three frameworks​

In rough order of sophistication:

  1. Test budget. Sized to produce enough data to learn whether a campaign or cluster works.
  2. Target CPA budget. Sized to deliver a specific number of conversions at a specific cost.
  3. Percent of revenue budget. Sized as a fixed percentage of revenue, where paid search competes against other line items.

Most teams use a mix as they mature.

Framework 1: test budget​

For a campaign you have never run before. The goal is data, not conversions.

How to size it​

Estimate two things:

  • Average CPC for the cluster (Google's keyword data, weighted toward the high end to be conservative).
  • Click volume needed for Google's algorithm to learn. Roughly 50 to 100 clicks per week minimum.

Multiply: CPC × clicks per week × 4 weeks ≈ monthly test budget.

For B2B SaaS clusters with $5 to $20 CPCs and a 75 click per week target, the result is in the $1,500 to $6,000 monthly range.

When to stop testing​

After 2 to 4 weeks of data. By then you should know:

  • CTR (acceptable at 2 to 4 percent for most B2B SaaS).
  • Conversion rate (acceptable at 1 to 5 percent for sign-ups, lower for demos).
  • CPA (compared to your target).

If the campaign hits numbers you like, move to the scale phase. If not, stop it and try a different cluster, ad copy, or landing page.

Do not overinvest​

A common mistake: teams run a test campaign at $20,000/month "to give it a real chance." You do not need that to learn. You need just enough volume to see clean numbers. Save the bigger budget until you have signal.

Framework 2: target CPA budget​

For a campaign you understand well enough to size against a specific outcome.

The math​

Let:

  • C = your max acceptable CPA (cost per conversion).
  • CPC = the cluster's average cost per click.
  • CR = your conversion rate (conversions divided by clicks).
  • N = conversions you want per month.

Then: monthly budget = N × C, because CPA = CPC / CR.

If your CPA target is $200 and the cluster delivers $200 CPA at scale, every $200 you spend produces one conversion. If you want 50 conversions a month, budget $10,000.

What if CPA is above target​

If observed CPA is higher than your target, you have three options:

  • Lower CPA through better keywords, ad copy, or landing page. Often the right move first.
  • Accept higher CPA if downstream economics support it. A $400 CPA can be fine if customers are worth $20,000.
  • Stop using the cluster. Some clusters are just expensive. Move budget to a cheaper one.

Budget alone will not fix CPA. When you throw more budget at a campaign with bad CPA, you get more bad CPA.

When this framework breaks​

  • You do not know your CPA target. Common for early stage products. In that case, default to the test budget framework.
  • Conversion data is too thin to estimate CR. Run the test budget framework first, accumulate data, then switch to CPA targeting.
  • Conversions do not directly correlate with revenue. A sign-up CPA is meaningful only if some predictable percentage become customers. If the sign-up-to-customer rate is wildly variable, optimize on something further down the funnel.

Framework 3: percent of revenue budget​

For mature operations where paid search is one channel among many.

How it works​

Pick a target marketing spend as a percentage of revenue (often 10 to 30 percent of ARR for early-stage SaaS, lower for mature companies). Within that, allocate a percentage to paid search, based on its proven efficiency relative to other channels.

If you have $5M ARR, target 20 percent for marketing ($1M total), and paid search gets 30 percent of that ($300K, or $25K/month), your Google Ads budget is $25K/month, split across campaigns.

When this works​

  • You have multiple proven channels and need to allocate among them.
  • You are managing to a CAC payback or LTV/CAC target at the company level.
  • Finance wants stable, predictable spend.

When this breaks​

  • You are earlier stage and do not have stable revenue. Percent of revenue budgets shrink when revenue dips. That is exactly when you need new customers most.
  • Your channels have different maturity. If you spend 30 percent of your marketing budget on Google Ads before it is proven, you bet on an unknown channel.

The starting point​

If you start fresh:

  • Run the test budget framework for 6 to 8 weeks across 3 to 5 clusters.
  • Identify the one or two clusters that convert at a reasonable CPA.
  • Move to target CPA budget on those, and scale up to your target volume.
  • Add percent of revenue framing once paid search is one of several proven channels and you manage at the portfolio level.

This trajectory takes 3 to 6 months for most B2B SaaS. Do not try to skip steps.

Common budget mistakes​

Daily budget too low to win auctions​

A daily budget of $20 in a cluster with $10 CPC means you will get 2 clicks on a good day, often zero. Either accept that the campaign will not generate meaningful data, or raise the budget.

Daily budget too high for a learning phase​

If you run $500/day on a brand-new campaign, you will burn $15,000 before the algorithm learns what works. You will learn just as well from $5,000, and you will have $10,000 left for the campaign that performs.

Do not change budgets too often​

Google's algorithm needs days to recalibrate after a budget change. Frequent changes (weekly or more) prevent it from ever stabilizing. Set the budget. Leave it for at least 2 weeks. Then evaluate it.

Do not treat budget as the lever​

Budget sets a ceiling. Keywords, ad copy, landing page, and bidding strategy determine performance. If your campaign does not work at $1,000/month, it will not work at $5,000/month either.

How Hero Marketer suggests budgets​

The campaign wizard suggests a monthly budget when you reach the budget step. The suggestion is sized for the "test budget" framework: enough volume for Google to learn, not optimized for a specific CPA target.

You can override the suggestion. See Set your budget for the in-product details and How budget suggestions are calculated for the math.

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