Investors ask healthtech founders the same early question: how long does it take to earn back what you spend to win a customer? The answer, CAC payback, sounds simple. In practice a hospital software company, a consumer health app and a doctor marketplace each need a different formula, and applying the generic software version to all three produces numbers that mislead the founder as much as the investor.
This article is for health tech founders, growth leads and finance owners preparing board packs or fundraising material in India. It sets out the formula for each model, a worked example with hypothetical figures, and the traps that distort the result. All numbers below are invented to show the arithmetic. They are not benchmarks, and you should not copy them into a deck.
The basic formula
CAC payback is the number of months of gross profit needed to recover the cost of acquiring a customer.
Payback months = CAC divided by (monthly revenue per customer multiplied by gross margin).
Two details matter. First, use gross margin, not revenue. A hospital software company that spends heavily on implementation and support earns far less gross profit per rupee of revenue than the invoice suggests. Second, use fully loaded CAC: marketing spend, sales salaries and commissions, tools, demos, pilots, travel and the cost of sales engineering. A figure that counts only advertising spend is a media cost per customer, not CAC. Our glossary entry on patient acquisition cost covers the consumer-side definition.
Calculate on a cohort basis: the customers acquired in one period, with the spend that produced them, followed forward. Dividing last month's spend by last month's new customers hides the lag between spend and signature, which in B2B can be several months.
Model 1: B2B sales to hospitals and clinics
A company selling software, devices or services to hospitals has a long sales cycle, committee decisions, pilots and slow implementation. The revenue clock does not start at the first meeting.
Formula. CAC for the cohort = all sales and marketing cost over the period that produced the cohort, including the months before signature. Payback = CAC divided by (monthly recurring revenue per account multiplied by gross margin), counted from the date billing starts, not the date of signature.
Worked example (hypothetical). A startup sells a bed-management product. Over two quarters it spends 48 lakh rupees on sales salaries, marketing, travel and pilot support. It signs eight hospitals. CAC is therefore 6 lakh rupees per hospital. Each pays 60,000 rupees a month. Gross margin is 0.65 after hosting, support staff and onboarding. Monthly gross profit per account is 39,000 rupees. Payback is 6,00,000 divided by 39,000, or about 15.4 months.
Traps specific to this model.
- Pilot cost. Free or discounted pilots are acquisition cost. Many founders leave them out because no invoice is involved. Include staff time and any discount.
- Billing lag. If signature is month 0 but billing starts in month 4 after integration, the payback clock starts at month 4. Measure both "time to sign" and "time to first invoice".
- Churn at renewal. Annual contracts hide churn until month 12. If one of the eight accounts leaves at renewal, the effective CAC per retained customer is higher.
- Concentration. One large hospital group can make payback look good while smaller accounts never pay back. Report by account size.
- Implementation costs counted as revenue. One-time fees are not recurring. Keep them separate, and treat any margin on them as an offset to CAC, not as monthly revenue.
Model 2: D2C consumer health
Here the customer is an individual: an app subscriber, a diagnostic package buyer or a teleconsultation patient. Acquisition is mostly paid media, referral and organic channels, with a short path to purchase.
Formula. Blended CAC = total acquisition spend divided by all new paying customers. Paid CAC = paid spend divided by customers attributed to paid. Payback = CAC divided by monthly gross profit per customer, adjusted for how many customers are still active each month.
Worked example (hypothetical). A consumer app spends 10 lakh rupees in a month on paid acquisition and 2 lakh rupees on creative and tools. It gains 4,000 paying subscribers. Blended CAC is 300 rupees. Each pays 199 rupees a month, with gross margin of 0.80 after payment fees and clinician cost, giving 159 rupees of gross profit per month. Naive payback is 300 divided by 159, or 1.9 months.
Now apply retention. Suppose only 3,000 of those subscribers are still paying in month 2 and 2,000 in month 3. The cohort's cumulative gross profit per original subscriber is about 159 in month 1, 119 more in month 2, and 80 more in month 3. After three months it has reached 358, so the cohort passes the 300-rupee CAC during month 3. Payback is therefore close to 2.8 months, not 1.9.
Traps specific to this model.
- Blended versus paid. Organic and referral customers lower blended CAC and hide the cost of paid growth. Report both, and watch the paid number as you scale because incremental customers cost more.
- Free trials. Count trial users who never pay as part of the cost of acquiring those who do.
- Refunds and failed payments. Subtract them from revenue.
- Clinician cost in gross margin. If every consultation uses doctor time, that is cost of goods, not overhead.
- Platform fees on app stores. Subscription revenue via an app store carries a commission, which lowers margin.
- Health-marketing rules. Aggressive claims to hit CAC targets invite regulatory trouble. Keep creative within ASCI and Meta/Google health policy; see our healthcare startup marketing page and the digital health marketing article.
