CAC Payback Period: How Much SaaS Should Spend on Ads

This post works backwards from your unit economics to two numbers: the CPA you can afford at each funnel stage and the monthly ad budget that follows from it. It reuses the funnel logic from which SaaS event to bid on, and it’s the subscription counterpart to what one-off ROAS hides.

What should SaaS CAC include?

Customer acquisition cost is what you spend to win one paying customer. Two versions answer different questions.

Paid CAC covers the paid channel alone: ad spend, plus management fees and creative production, divided by the new paying customers that came from paid. Use it to decide how much more to put into Google Ads and Meta.

Blended CAC divides all sales and marketing cost by all new paying customers, including organic, referral and word of mouth. It tells you what the business as a whole pays for a customer. It also flatters paid: a month with a burst of referral sign-ups lowers blended CAC while your ads cost the same.

In sales-led B2B, add sales cost to paid CAC: the share of sales salaries, commission and demo time that goes into closing paid-sourced deals. A $300 demo that needs $3,000 of sales effort to close costs you $3,300 plus the demos that didn’t close.

How do you calculate CAC payback?

CAC payback (months) = CAC / (new MRR per customer × gross margin %)

Use gross margin, not revenue. Hosting, support and payment fees come out of every subscription payment, and only what’s left pays back acquisition. Bessemer Venture Partners measures payback against gross-margin-adjusted revenue for that reason (Bessemer, 2021).

Turn the formula around and you get the number that drives your ad plan:

Allowable CAC = MRR per customer × gross margin % × target payback months

Say your plan costs $40 a month at an 85% gross margin. Each customer contributes $34 a month. If you can fund a six-month payback, the most you can pay for a customer is $204.

What is a good CAC payback period for SaaS?

Treat published numbers as benchmarks from investors’ portfolios, not as your target. In its State of the Cloud 2023 report, Bessemer rated CAC payback of 12–18 months as good, 6–12 months as better and 0–6 months as best (Bessemer, 2023). In 2021 it suggested targets by segment: under 12 months for SMB-focused companies, under 18 for mid-market and under 24 for enterprise, because enterprise customers pay more and churn less (Bessemer, 2021).

Your own limit comes from cash. A payback period is how long you finance each customer. If you have six months of runway, an 18-month payback means every customer you buy today pays you back after the money runs out.

Where does LTV:CAC fit next to payback?

Lifetime value is gross profit per customer over their whole lifetime. A quick version divides monthly gross profit by monthly churn. At $34 a month and 4% monthly churn, that’s $34 / 0.04 = $850. Against a $204 CAC, LTV:CAC is about 4.2.

Bessemer recommends investing in acquisition when LTV/CAC is 3x or more (Bessemer, 2021). Use LTV:CAC as a ceiling check and payback as the working constraint. LTV rests on a churn guess that a young product can’t confirm yet, and a one-point change in monthly churn moves the result a lot: at 5%, the same customer is worth $680. Payback needs only data from the months you’ve already seen.

Why do B2B and self-serve SaaS get different budgets?

Sales-led B2B has larger contracts, longer cycles and sales cost inside CAC. Customers churn slower, so you can carry a longer payback. Say a customer pays $500 a month at 80% gross margin ($400 a month in gross profit) and you aim for 15 months. Allowable CAC is $6,000. If closing a deal costs $3,000 in sales effort, $3,000 is left for the ads.

Self-serve, PLG and B2C SaaS have small plans, no sales cost and higher monthly churn. You need a shorter payback because fewer customers stay long enough for a long one to finish. The $40 plan above with a six-month target is a typical shape.

The faster cycle helps you too. A self-serve cohort shows its payback within months, so you can correct the budget within a quarter. A B2B account may wait two quarters to see whether last quarter’s demos closed.

How do you turn allowable CAC into a target CPA per funnel stage?

Multiply the ad-side allowable CAC by the rate at which each stage turns into a paying customer:

Target CPA at a stage = allowable paid CAC × (stage-to-paid conversion rate)

For the self-serve example, say 15% of trials pay and 37.5% of activated accounts pay (40% of trials activate):

• Paid customer: $204
• Activation: $204 × 0.375 = $76.50
• Trial start: $204 × 0.15 = $30.60

For the B2B example, say 40% of demo requests become SQLs and 25% of SQLs close (10% of demos close):

• Closed won: $3,000
• SQL: $3,000 × 0.25 = $750
• Demo request: $3,000 × 0.10 = $300

Set the target CPA on whichever stage you bid on, as chosen in the conversion event post. Recalculate it when the stage conversion rates move. If trial-to-paid drops from 15% to 12%, your affordable trial CPA drops from $30.60 to $24.48 even though nothing changed in the ad account.

How big does the monthly ad budget need to be?

Start with the customers you want, then check the volume the platforms need.

Monthly budget = new customers wanted / stage-to-paid rate × target CPA at that stage

Twenty new self-serve customers a month needs about 133 trials at $30.60, so about $4,080. Five B2B customers needs 50 demo requests at $300, so $15,000.

Then test the result against the platforms’ learning thresholds:

• Meta. An ad set usually exits the learning phase after about 50 optimization events in the week after its last significant edit (Meta Business Help Center). 133 trials a month is about 31 a week. To reach 50 a week on one ad set at $30.60, you need about $1,530 a week, or $6,600 a month.
• Google Ads. Google recommends judging target CPA on the last 30 days with at least 30 conversions (Google Ads Help). 133 trials a month is plenty for one campaign. 50 demos split across two campaigns gives each 25, so consolidate or accept slower learning.

If the budget your payback allows can’t feed the platforms, you have three honest options: bid on an earlier stage with values, consolidate into fewer campaigns and ad sets, or raise the budget and accept a longer payback while the account learns. Spreading a small budget across many campaigns gives you none of the three.

Google also notes that a campaign can spend up to twice its average daily budget on a given day (Google Ads Help). Plan cash on the monthly figure, not the daily one.

Why should you judge spend by cohort payback, not monthly ROAS?

Monthly ROAS divides this month’s revenue by this month’s spend. For a subscription, that punishes every new customer. The $40 customer you bought for $204 shows a first-month ROAS of about 0.2. On a one-off ecommerce dashboard, you’d cut that campaign.

Group customers by the month you acquired them instead. For each cohort, track ad spend in that month, customers won, and cumulative gross profit by month since acquisition. The cohort has paid back when cumulative gross profit passes the spend.

Churn makes the cohort view slower than the formula. With 4% monthly churn, the six-month formula above doesn’t hold: the cohort has earned about $185 per original customer after six months and passes $204 in month seven. Annual prepaid plans move cash payback earlier, but report them on monthly margin anyway so cohorts compare like for like.

Paid-sourced cohorts can also churn faster or slower than organic ones. Split the cohort table by acquisition channel once you have enough customers in each.

How often should you review CAC and payback?

• Weekly: platform CPA at your bid stage against its target. Act on it only after the campaign has enough conversions to judge.
• Monthly: paid CAC and blended CAC, and the cohort table updated with another month of gross profit.
• Quarterly: recalculate allowable CAC from current ARPA, gross margin and churn, then reset stage CPA targets and the budget.

We build this model for SaaS companies advertising on Google and Meta, and run the bidding through our Google Ads management. Want the numbers worked out for your funnel? Start with our free Profit Growth Plan.

FAQ

How do you calculate the CAC payback period?

Divide CAC by monthly recurring revenue per new customer multiplied by your gross margin. A $204 CAC on a $40 plan at 85% margin pays back in six months.

What is a good CAC payback for SaaS?

Bessemer’s State of the Cloud 2023 rated 12–18 months good, 6–12 better and under 6 best (Bessemer, 2023). These are benchmarks. Your real limit is how long you can afford to finance each customer.

Should CAC include sales costs?

Yes, when sales closes the deals. Count the sales salaries, commission and demo time spent on paid-sourced deals, or your CAC looks cheaper than it is.

How much should a SaaS company spend on ads?

Work out how many new customers you want, divide by the stage-to-paid rate, and multiply by the target CPA at that stage. Then check that each campaign or ad set gets enough conversions for the platform to learn.

What is the difference between paid CAC and blended CAC?

Paid CAC divides paid acquisition cost by customers from paid channels. Blended CAC divides all sales and marketing cost by all new customers, so organic growth lowers it.