Payback Period
Date: 2026-08-16
How long until an acquired customer has repaid what they cost. It’s the cash-flow constraint that LTV:CAC hides — and it’s what actually determines how fast you can grow, because you can’t spend money you haven’t got back yet.
What it is
Payback period is the time from acquiring a customer to recovering their acquisition cost from their cumulative contribution.
On the running model — £22.50 CAC, £15 contribution per order, second order at around four months:
month 0 order 1 +£15.00 cumulative £15.00 ← still £7.50 down
month 4 order 2 +£15.00 cumulative £30.00 ← paid back
month 14 order 3 +£15.00 cumulative £45.00
payback ≈ 4 months
The first order doesn’t cover acquisition. Every new customer is cash-negative until they come back — which makes repeat purchase the mechanism that funds growth, not just a nice-to-have.
Why it constrains growth more than the ratio does
LTV:CAC says whether a customer is worth acquiring. Payback says how fast you can acquire the next one, because the money is tied up until it returns.
£100,000 of working capital, £22.50 CAC
payback 4 months → recycle 3× a year → ~13,300 customers/yr
payback 12 months → recycle 1× a year → ~4,400 customers/yr
Same LTV:CAC, three times the growth rate. Payback is the difference, and no amount of favourable lifetime economics compensates for it without external funding.
In plain terms: a customer who’s profitable over three years is still money you don’t have for three years. Growth speed is set by how quickly the money comes back, not by how much eventually does.
What good looks like
Depends entirely on how you’re funded and on the category:
| Payback | Position |
|---|---|
| First order | Self-funding. Growth limited only by demand |
| Under 6 months | Comfortable for most retailers |
| 6–12 months | Workable with reserves or facilities |
| Over 12 months | Needs external funding, or growth is capped |
A considered-purchase category with a long repurchase cycle will have long payback structurally — that’s the business, not a failing. What matters is whether the funding matches.
Improving it
Ordered by how directly they act on the constraint:
- Raise first-order contribution. Increase AOV, improve margin, reduce fulfilment cost. Every pound here comes back immediately — Contribution Margin, Average Order Value
- Bring the second order forward. A well-timed replenishment or post-purchase flow shortens payback without changing lifetime value at all — Replenishment Timing, Lifecycle Messaging
- Reduce CAC, particularly by shifting mix towards channels with faster-paying customers
- Reconsider first-order discounting. A £10 welcome code is £10 of acquisition cost — book it in CAC or deduct it from first-order contribution, never both, which double-counts it. It lengthens payback more than it appears to for a different reason: it’s paid to every new customer, including those who’d have come anyway, so the cost per incremental customer is many times £10 — Incrementality Testing
That last one is the trap worth naming: welcome discounts are the most common lever for acquisition volume and the most damaging for payback.
Measuring it
- Cohort-based. Take a month’s new customers and track cumulative contribution against their acquisition cost — Cohort Analysis
- Contribution, not revenue. Revenue payback is meaninglessly fast
- Include everything in CAC, discounts included — Customer Acquisition Cost
- Segment by channel. Payback varies more by acquisition source than almost any other metric, and the channel with the best CAC often has the worst payback
Where it fits
Read alongside LTV to CAC Ratio — the ratio answers “is this worth doing”, payback answers “can we afford to do it at this rate”. A business can pass one and fail the other, and it’s failing the second that causes actual insolvency.
Assembled with the rest in Guide - Unit Economics and Commercial Decisions.