Lifetime value is the number that makes a unit economics slide work, and it is three assumptions stacked on top of each other.
LTV = average order value × orders per year × years retained
Sixty dollars an order, four orders a year, three years retained, and the lifetime value calculator gives $720, with $240 of revenue a year per customer. Against a $240 cost to acquire, that is the 3:1 ratio every investor deck reaches for.
It is revenue, not profit
The LTV formula multiplies order value, and order value is revenue. Apply a 30 per cent margin and the $720 becomes $216 of gross profit over three years, against $240 spent to acquire the customer. The business loses $24 per customer while hitting the benchmark exactly.
The 3:1 rule was always meant to be applied to gross profit LTV rather than revenue LTV. The version in circulation drops that word, and dropping it moves the answer by the whole margin. On a 30 per cent margin, a 3:1 revenue ratio is a 0.9:1 profit ratio, and the true benchmark would need a ratio of 10:1 on revenue to reach 3:1 on profit.
Then there is when the money arrives
Even with healthy margins, the ratio says nothing about timing. That $216 of gross profit arrives at roughly $72 a year, so the $240 acquisition cost is repaid in about three years and four months, which is longer than the three year lifespan the LTV assumed in the first place.
This is the difference between a business that is profitable on paper and one that runs out of cash. Every new customer is a cash outflow now against an inflow spread over years, so growing faster makes the cash position worse, not better, until payback shortens. Companies die in that gap while their unit economics slide is accurate.
Payback period is the number to put beside the ratio. It is the one a lender or a board will ask for, and it is the one that decides how fast you can afford to grow.
The lifespan is the softest input
Order value is measured, and the AOV calculator takes it straight from revenue and order count. Purchase frequency is measured. Customer lifespan is almost always an estimate, and for a young business it is an estimate about a period longer than the business has existed.
Its leverage is total. Cut the lifespan from three years to one and the LTV falls from $720 to $240, which is the entire acquisition cost. Cut frequency from four orders a year to one and it falls to $180. Neither of those is a pessimistic scenario; they are what happens when a cohort behaves slightly worse than the first one did.
The useful discipline is to run the number three ways: measured, conservative, and what it would take to break even. For that last one, break-even units works in the other direction, from fixed costs and contribution margin to the volume that covers them. Against a $40 price and $22 of variable cost, $5,000 of fixed costs needs 278 units, and that is a figure nobody has to assume anything about.
For the acquisition side of the ratio, cost per acquisition is where the denominator comes from, and break-even ROAS covers the same margin trap from the advertising end.