Payback period: how long until a purchase pays for itself

Payback period is the time it takes for an investment to return the cash it consumed. It is the crudest of the investment measures and the most used, because it answers the question a small business actually asks — how long before this stops being a hole in the bank account — rather than the question textbooks prefer.

Calculating a payback period

• Total the cash out: purchase price, installation, training, disruption during changeover.
• Total the cash in per period: savings, additional margin, avoided costs — in cash rather than in accounting profit.
• Divide, or run the cumulative figure month by month until it crosses zero, which is more honest where returns are uneven.
• Use incremental amounts only: what changes because of this decision, not what the department spends overall.
• Ignore depreciation, since it is not cash, and this measure is about cash.

What it deliberately ignores

Everything after the payback point, which is its central weakness. A machine paying back in two years and lasting three is worse than one paying back in three years and lasting fifteen, and payback period cannot see the difference. It also ignores the time value of money and any residual value at disposal. That makes it a poor sole criterion for large or long-lived purchases — and a perfectly reasonable screen for small ones, where the analysis should not cost more than the decision.

Be sceptical of savings that depend on somebody having spare time afterwards. «This saves four hours a week» is only cash if those four hours are removed from a wage bill or sold to a customer; otherwise it is a genuine improvement in working life that belongs in a different column of the argument.

When payback is the right test

1. Small purchases where a full appraisal costs more than the asset.
2. Decisions with genuine cash constraints, where running out before the return arrives is the actual risk.
3. Technology with a short useful life, where anything beyond three years is speculative anyway.
4. Comparing similar options, where the ignored factors are roughly equal across them.
5. Not for anything long-lived, strategic or with a large residual value — use a discounted measure for those.

Ettex Sheets holds the cumulative cash profile month by month, which is both the calculation and the sanity check — seeing the line cross zero is more informative than the single figure it produces. Where the purchase is large enough to matter, the same sheet should carry the assumptions, since those are what any later review will question.