Investment payback period: practical guide

What to prepare

• Gather supplier quotes, invoices, time records and the actual scope of the job or business decision.
• Separate revenue from VAT, direct costs from overheads, and profit from the timing of cash receipts.
• Use the same accounting period and currency for related inputs.

Understand the inputs

The calculation method

Simple payback = investment ÷ annual benefit. Discounted payback accumulates discounted benefits and interpolates within the recovery year.

Worked example

Illustrative inputs and their result.

Example inputs

Initial investment (€)

40000

Annual net cash benefit (€)

12000

Annual discount rate (%)

8

Discounted model horizon (years)

20

Calculated example result

Simple Payback Years

3.3333 years

Discounted Payback Years

4.0312

How to interpret the result

A profitable estimate can still create a cash shortfall. Read the cost and timing assumptions as well as the headline profit, price or return; the result is a scenario, not a sales forecast.

Keep the scope constant while changing price, volume, supplier cost or time. A lower-sales or higher-cost case helps show whether the decision depends on an optimistic assumption.

Common mistakes to avoid

• Do not confuse markup on cost with margin on selling price.
• Include work that is easy to miss, such as travel, setup, rework and administration, where the model supports it.
• Do not treat tax collected or an unpaid invoice as freely available cash.

Assumptions and sources

A blank discounted result means the entered horizon does not recover the investment. Benefits after payback are not considered by this metric.

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• Break-even analysis: practical guide
• Irish corporation tax: practical guide
• Customer acquisition & value: practical guide
• Stock turnover & DSO: practical guide