cash ÷ net burn = runway
Startup Runway Calculator
Calculate your startup's runway and burn rate: enter cash, revenue, expenses and growth to see months left, your zero-cash date and break-even month.
SaaS Unit Economics Calculator: LTV & CAC
Check whether each customer is worth what it costs to win. Four inputs give you lifetime value, LTV:CAC and how many months it takes to earn back acquisition spend.
- LTV:CAC ratio
- 2.6 : 1
- Customer lifetime value (LTV)
- €3,168
- CAC payback period
- 15.2 months
- Average customer lifetime
- 40.0 months
- Gross profit per account
- €79.20/ month
- Annual churn equivalent
- 26.2%
Positive, but thin: little room for rising acquisition costs.
LTV = ARPA × gross margin ÷ monthly churn. Payback = CAC ÷ (ARPA × gross margin).
A ratio around 3:1 and a payback well under 12–18 months are widely used rules of thumb, not laws. They vary by market, contract length and growth stage.
Runs entirely in your browser. No data is sent to a server.
How it works
- Enter your average monthly revenue per paying account (MRR ÷ customers).
- Add your gross margin and monthly customer churn rate.
- Enter the customer acquisition cost: sales and marketing spend divided by new customers in the same period.
- Read LTV, LTV:CAC and CAC payback. Try different churn values to see how sensitive the result is.
FAQ
How do you calculate LTV for a SaaS business?
A common simple formula is ARPA × gross margin ÷ monthly churn rate. With €99 ARPA, 80% gross margin and 2.5% monthly churn, LTV is about €3,168.
What is a good LTV:CAC ratio?
Around 3:1 is the most widely quoted rule of thumb. Below 1:1 you lose money on every customer; far above 5:1 can mean you are under-investing in growth.
How do you calculate CAC payback period?
Divide CAC by the monthly gross profit per customer (ARPA × gross margin). €1,200 CAC and €79.20 monthly gross profit give a payback of about 15 months.
Why does churn have such a big effect on LTV?
Average lifetime is 1 ÷ churn, so halving churn doubles lifetime and LTV. Small errors in the churn estimate therefore change the result a lot, especially for young startups with little data.
Should LTV use revenue or gross margin?
Using gross margin is more conservative and closer to the cash a customer really contributes. Revenue-based LTV looks larger but overstates what you can afford to spend on acquisition.