Free SaaS metrics calculators

There are dozens of SaaS metrics and it is possible to track all of them while understanding none. In practice five numbers determine whether a subscription business works, and they are interdependent enough that looking at any one in isolation will mislead you.

Unit economics: does a customer pay for themselves?

LTV:CAC is the headline answer, and CAC payback is the one that determines whether you can afford to grow this month. A business at 5x LTV:CAC with a 30-month payback still needs a large bank balance to scale, because it is funding each cohort for two and a half years before the cash comes back. High ratio and slow payback is the most common way founders are surprised by a cash crunch.

Retention: is the bucket leaking?

Churn drives everything downstream. It sets customer lifetime, which sets LTV, which sets the LTV:CAC ratio. A single percentage point of monthly churn is worth more than most pricing experiments: going from 3% to 2% monthly churn extends average customer lifetime from 33 months to 50, which raises LTV by half at identical ARPU. Retention is also the cheapest thing to fix, because it requires no additional acquisition spend.

Growth: is acquisition compounding?

Quick ratio combines the growth and churn views into one number: MRR gained divided by MRR lost. It is the fastest way to see whether the sales team is rowing forward or just keeping the boat still. Below 2x, churn is consuming most of your new revenue, and the fix is retention rather than more spend.

Solvency: how long have you got?

Runway is a constraint rather than a goal, but it is the constraint that ends companies. Twelve months is the practical minimum, eighteen the common target, and fundraising should begin with nine months remaining because the process takes three to six to close. If you are already profitable the calculator says so, which is a genuinely different situation from a long runway: the constraint becomes how aggressively to invest rather than how long you can survive.

Reporting: what is the recurring revenue?

MRR is the input to almost everything else, and it is the metric most often measured incorrectly — usually by booking annual contracts as a single month, which inflates the figure twelvefold in the month the cash lands. Getting MRR right, including amortising annual plans and building the net new MRR waterfall, is the foundation the other five calculators stand on.

How to use these calculators together

Start with MRR and ARPU, because it feeds the others. Then churn, because it determines lifetime. Those two give you LTV:CAC and payback, which together tell you whether growth is affordable. Quick ratio tells you whether it is working, and runway tells you how long you have to find out.

The order to read them in

These six are not a menu, they are a chain. Each one takes the previous one’s output as an input, so reading them out of order produces numbers that cannot be checked against each other:

LTV:CAC → CAC Payback → Quick Ratio → MRR → Churn → Runway

1. MRR and ARPU come first in a literal sense — they are the revenue input to everything else, and the annual-plan amortisation error (booking $1,200 as $1,200) propagates into all five other metrics at once.
2. Churn comes next, because customer lifetime is 100 ÷ churn and lifetime is the multiplier on LTV. No other input has that much leverage on the unit economics.
3. LTV:CAC then answers the profitability question, and CAC payback answers the cash question about the same two inputs. A ratio is not useful without a payback, and a payback without a ratio can flatter a channel that never breaks even.
4. Quick ratio reports on the whole engine: whether the growth you are paying for is outrunning the churn you are suffering. It is the one number to check monthly once the others are set up.
5. Runway is the constraint on all of it — how many months you have to act on whatever the first four told you.

A worked pass through the chain: MRR $40,000 across 400 customers gives ARPU $100; 3% monthly churn gives a 33-month lifetime; at an 80% margin LTV is $2,640; against a $450 CAC that is a 5.9x LTV:CAC and a 5.7-month payback; a quick ratio of 4.1x says growth is comfortably outrunning churn; and $450,000 of cash against $29,000 of net burn gives 15.5 months of runway to keep doing it. Each figure is an input to the next, and any one of them read alone could be made to look good.

What these calculators do not do

They do not connect to your billing system, and they do not store anything you type — every figure is computed locally in your browser from inputs you supply. That is a deliberate trade: it makes the tools instant and free, and it means every number is only as good as what you put in. Treat the output as a planning aid, not as financial advice, and re-run the chain whenever pricing, hiring or your acquisition mix changes.