Payback Period

The computation is arithmetic, not algebraic. Lay out the project's expected net cash flows by period, starting with the initial outlay as a negative amount at time zero, then accumulate. The payback period is the point at which the running total first turns non-negative. When the recovery falls inside a year, convention interpolates: take the number of full years before recovery, then add the unrecovered balance at the start of that year divided by the cash flow received during it.

A project costing 1,000 that returns 300, 400 and 500 has cumulative balances of minus 700, minus 300 and plus 200. Recovery occurs in year three, so payback is two years plus 300 divided by 500, or 2.6 years. The fractional part embeds an assumption that cash arrives evenly through the year, which rarely holds for lumpy contract or seasonal flows.

Discounted payback accumulates present values rather than nominal amounts, so recovery is measured against a schedule that respects the required rate of return. The result is always at least as long as simple payback, and a project may never achieve discounted payback even though its nominal cash flows sum above the outlay.

The repair is partial. Discounting corrects the treatment of timing within the recovery window but says nothing about the periods after it. A project whose discounted flows turn cumulative-positive in year four could still carry a large decommissioning or reinvestment outflow in year eight that drags net present value below zero. Only where every post-recovery discounted flow is non-negative does achieving discounted payback within the project life imply positive net present value.

Payback survives because it answers a question net present value does not: how long is capital exposed. Firms with tight liquidity, covenant-constrained balance sheets or limited access to external funding care about the speed of cash recovery independent of value creation. The measure also acts as a crude risk proxy in settings where forecast reliability decays sharply with horizon, such as emerging-market projects, fashion-driven consumer products or technology with short obsolescence cycles.

It appears in vendor sales material, energy and equipment procurement, and internal hurdle policies that pair a maximum acceptable payback with a minimum net present value. The cutoff itself is the weak point: it is set by management judgement rather than derived from the cost of capital, so it carries no theoretical anchor and varies widely across firms and divisions.

Candidates should be able to construct the cumulative schedule from a table of uneven cash flows, interpolate the fractional year correctly, and repeat the exercise on discounted flows using a stated required return. Expect items that compare two projects where payback and net present value rank them differently, usually because the shorter-payback project has a truncated cash flow profile while the longer one delivers heavily in later years.

Be precise about the criticisms and their scope: simple payback ignores both the time value of money and all cash flows beyond recovery, while discounted payback addresses only the first. Know that neither measure is additive across projects, neither indicates the scale of value created, and that the accept-reject threshold is arbitrary. Net present value remains the criterion consistent with shareholder wealth maximisation.