Payback Period

Payback period is the time required to recover the initial investment from cash inflows. It answers: how long until I get my money back? Payback is used in capital budgeting and customer economics to assess liquidity risk and compare projects. It does not account for the time value of money or returns beyond the payback point.

Formula

Simple payback:

Payback Period = Initial Investment / Annual Cash Inflow

When cash flows vary by year, add inflows until the cumulative total equals or exceeds the initial investment. The payback period is the point at which that occurs. For customer acquisition, payback period = CAC / (ARPU × Gross Margin) per month or year.

Example

An equipment purchase costs $60,000 and generates $15,000 per year in net cash flow. Payback period = $60,000 / $15,000 = 4 years. For customer economics: CAC is $120, and each customer contributes $30/month in gross margin. Payback = $120 / $30 = 4 months.

Relationship to ROI

Payback period and ROI provide different information. ROI measures total return over the full life of the investment; payback measures how quickly capital is returned. A project can have a short payback but modest ROI, or a long payback but high ROI. Payback is often used as a risk screen: shorter payback implies faster capital recovery and less exposure to uncertain future cash flows.

Limitations

Simple payback ignores the time value of money: a dollar received in year 1 is worth more than a dollar in year 5. Discounted payback addresses this by discounting cash flows. Payback also ignores cash flows after the payback point, so it can favor short-lived projects over more valuable long-term ones. IRR and NPV are more comprehensive for project comparison.