Find how long it takes to recover an investment from monthly net profit.
Payback period (months) = Investment ÷ Monthly net profit.
Payback period — how long it takes an investment's returns to recoup its initial cost — is popular precisely because it's simple and intuitive, but that simplicity hides a real analytical flaw: it treats a rupee received next year exactly the same as a rupee received in year five, ignoring the time value of money entirely. In reality, money available sooner is worth more than the same amount later, since it can be reinvested, and standard (non-discounted) payback period doesn't account for that at all — it just adds up raw cash flows until they equal the initial investment, with no discounting for when each rupee actually arrives.
An even more consequential blind spot: payback period completely ignores everything that happens after the payback point is reached. Two investments can have an identical 3-year payback period while one generates strong returns for another 10 years afterward and the other stops producing any cash flow at all right after year 3 — payback period alone would rank them as equally attractive, which is clearly wrong. This is exactly why payback period is best used as a quick, first-pass liquidity/risk screening tool (how fast do I get my capital back, which matters for cash-flow-constrained decisions) rather than a standalone investment-ranking metric — a more complete method like Net Present Value (NPV), which discounts every future cash flow to present value and accounts for the investment's entire life, is the more theoretically sound tool when comparing which of several investments is genuinely more valuable, not just which recovers cash fastest.
It ignores the time value of money — treating a rupee received next year identically to a rupee received five years from now, when in reality money available sooner is worth more since it can be reinvested. Standard payback period doesn't discount future cash flows at all.
Because it ignores everything that happens after the payback point. Two investments with an identical 3-year payback period can have very different total value if one keeps generating strong cash flow for another decade while the other stops entirely — payback period alone treats them as equally good, which misses the real difference in total return.
It fixes the time-value-of-money issue by discounting future cash flows before adding them up, but it still shares payback period's other limitation — ignoring any cash flows that happen after the payback point is reached. It's an improvement, but not a complete substitute for a method like NPV.
As a quick first-pass screening tool, especially when liquidity or cash-flow risk matters more than total long-term value — for example, comparing how fast different options return invested capital when capital is genuinely constrained. For deciding which investment creates the most total value, NPV (which discounts all future cash flows and accounts for the investment's full life) is the more theoretically sound choice.