NPV Calculator
Calculate Net Present Value of an investment to determine viability.
What this calculator does
Net present value asks whether a project is worth more than it costs, once you allow for the fact that money arriving in the future is worth less than money today. Each future cash flow is discounted back to the present and totalled, then the initial outlay is deducted.
The answer comes in pounds. Positive means the project is expected to add value above your required return; negative means it destroys value against the alternative use of the same capital. Unlike payback period or simple ROI, NPV takes timing seriously, which is why it remains the standard appraisal technique.
When to use it
NPV suits any decision where cash flows arrive across several years and their timing matters — buying machinery, opening a site, acquiring a buy-to-let, or choosing between projects with different shapes. It is also the right way to compare a lump sum offered now against instalments spread over time.
It matters most when the choice is finely balanced. Obviously good and obviously bad projects need no analysis. When two options look similar on undiscounted totals, discounting is usually what separates them, and the gap it reveals is often considerably larger than intuition suggests.
Understanding the inputs
The starting amount is your initial outlay at time zero, entered undiscounted. Annual return is the discount rate — the return you require given the risk involved, not the return you would like. Choosing this badly is the commonest way an NPV ends up misleading.
Years is the appraisal horizon. Be cautious about stretching it, since forecasts beyond five years carry little genuine information and a long horizon can rescue a marginal project on speculative later cash flows alone. The monthly addition field allows recurring contributions or ongoing costs to be modelled across the period.
How is this calculated?
NPV = Σ [CFt / (1 + r)^t] − Initial Investment. Positive NPV = profitable investment.
A worked example
A company is weighing up equipment costing £120,000 that should produce £34,000 of additional after-tax cash flow each year for five years. Its cost of capital is 8 percent.
The five-year annuity factor at 8 percent is 3.9927, so the present value of the cash flows is £135,752. Deducting the £120,000 outlay leaves an NPV of £15,752 — positive, so the project clears the hurdle. Undiscounted, the cash flows total £170,000, which makes the project look £34,000 better than it really is.
Limitations and assumptions
NPV is only as reliable as the cash flow forecasts behind it, and forecasts are opinions with decimal places. The mathematical precision of the technique can lend unearned confidence to inputs that are essentially estimates, especially from year three onward.
It assumes one constant discount rate, that interim cash flows can be reinvested at that rate, and that the project proceeds as planned. It places no value on the option to abandon, expand, or defer. Past returns do not predict future ones, and nothing here is investment advice.
Common Questions
- What does net present value mean?
- It is the value in today's money of all the future cash a project will generate, less what it costs to begin. A positive NPV means the project should create value above your required return. A negative NPV means the capital would do better elsewhere, whatever the accounting profit suggests.
- What discount rate should I use?
- For a company, the weighted average cost of capital, which blends the returns debt and equity providers require. For a personal decision, the return available from the next best alternative — a global tracker or paying down a mortgage, for example. The rate must reflect the risk of the project itself.
- Why is the discount rate so influential?
- Because it compounds against every future year. At 5 percent, a pound received in ten years is worth 61p today; at 12 percent it is worth 32p. Long-dated projects are acutely sensitive to the rate, which is why testing a range rather than committing to one figure is standard practice.
- Is a positive NPV always a go-ahead?
- No. NPV assumes your forecasts are sound, and forecasts for years four and five are usually optimism dressed as data. It also ignores capital rationing, execution risk, and strategic considerations. Treat a positive NPV as necessary but not sufficient, and always model what happens if revenue lands twenty percent short.
- How does NPV differ from IRR?
- NPV answers in pounds, IRR in a percentage. NPV requires you to supply a discount rate; IRR calculates one. When the two disagree — usually on projects of different sizes or with differently shaped cash flows — finance theory says trust NPV, because it measures the actual value created.
- Should the initial investment be discounted?
- No. It sits at time zero, undiscounted, because you are spending it now. Discounting the initial outlay by a year is a common error that understates the cost and flatters the NPV. Cash flows occurring during the first year are discounted once, at the end-of-year convention.
- How should I treat corporation tax?
- Forecast cash flows after tax and use an after-tax discount rate so the two are consistent. Capital allowances, including full expensing on qualifying plant and machinery, reduce the tax payable rather than appearing as a cash outflow themselves, so their benefit enters through a lower tax line in the relevant year.
- How do I handle residual or terminal value?
- Add it as an inflow in the final year alongside that year's operating cash flow. For an ongoing business, terminal value is often the final year's cash flow divided by the discount rate minus the long-run growth rate. It frequently dominates the answer, so its assumptions deserve the most scrutiny.
- Does NPV allow for inflation?
- Only if you are consistent. Either project nominal cash flows and discount at a nominal rate, or project real cash flows and discount at a real rate. Both work and give the same result. Combining real cash flows with a nominal discount rate is a frequent error that badly understates NPV.