A machine supplier tells you their new packaging line will pay for itself in three years. Your production manager wants it. The bank manager wants to see numbers before extending your overdraft to cover the deposit. And you are left trying to work out whether spending £120,000 today is genuinely a good use of the business’s cash, or just an expensive way to make the factory floor feel more modern. This is one of the most common decisions SME owners face, and it is also one of the easiest to get wrong, because ‘gut feel’ and ‘it pays for itself eventually’ are not the same as ‘this makes financial sense’. This article shows you three simple, well-established tools — payback period, net present value (NPV) and internal rate of return (IRR) — that let you test any capital purchase with real numbers, so the decision stands up to scrutiny from your accountant, your bank and your own conscience.
The Problem With ‘Does It Pay For Itself?’
Most business owners instinctively reach for one question when weighing up a big purchase: how long until this money comes back to me? That is a reasonable starting point, but it only tells half the story. £120,000 recovered in three years sounds good, but it depends entirely on what happens in years four and five, and on the fact that £1 received next year is worth less than £1 in your bank account today, because you could have invested, saved or used that £1 for something else in the meantime. Relying purely on ‘time to break even’ can lead you to reject a genuinely profitable machine in favour of one that merely looks quicker to repay. The three tools below fix that blind spot by putting a proper value on money over time, not just counting years.
Three Ways to Test an Investment
Payback period simply asks: how many years of cash inflows does it take to recover the original outlay? It is quick to calculate and easy to explain to a bank manager, but it ignores anything that happens after the cash is recovered and it ignores the time value of money entirely. Think of it as a rough screening test, not a final verdict.
Net present value (NPV) is the more rigorous tool. It takes every future cash inflow the machine or project will generate, ‘discounts’ each one back to today’s value using a rate that reflects your cost of borrowing plus a margin for risk, adds them all up, and subtracts the initial cost. If the result is a positive number, the project is expected to add that many pounds of value to your business, over and above what your money would have earned elsewhere. If it is negative, the project destroys value even if it looks profitable on paper.
Internal rate of return (IRR) answers a slightly different question: at what discount rate would this project’s NPV be exactly zero? In plain terms, it is the effective annual return the project generates. If your IRR comes out at 17% and your business borrows at 8%, that gap is your margin of comfort. IRR is useful because it converts a pounds-and-pence answer into a percentage that is easy to compare against your cost of finance or other opportunities.
The discount rate is simply the return you could reasonably expect elsewhere, adjusted for risk. If your business borrows at around 7% and you want a sensible margin for uncertainty, a discount rate of 10% to 12% is a reasonable starting point for most SME equipment decisions. Choosing a higher rate makes it harder for a project to show a positive NPV, so resist the temptation to pick a low rate simply to make a project look better than it is.
Worked Example: The £120,000 Packaging Machine
Suppose your business is considering a new packaging machine costing £120,000, installed and ready to run on 1 January. You expect it to generate the following additional net cash inflows over its five-year useful life, after accounting for extra staff time, materials and maintenance: £35,000 in year one, £40,000 in year two, £42,000 in year three, £38,000 in year four and £30,000 in year five. Using a discount rate of 10% to reflect your cost of finance plus a margin for risk, here is how the cash flows look once discounted back to today’s value.
| Year | Net Cash Flow | Discount Factor (10%) | Present Value |
|---|---|---|---|
| 0 | (£120,000) | 1.000 | (£120,000) |
| 1 | £35,000 | 0.909 | £31,815 |
| 2 | £40,000 | 0.826 | £33,040 |
| 3 | £42,000 | 0.751 | £31,542 |
| 4 | £38,000 | 0.683 | £25,954 |
| 5 | £30,000 | 0.621 | £18,630 |
| Present value of year 1 to 5 inflows | £140,981 |
| Less: initial cost of machine | (£120,000) |
| Net Present Value (NPV) | £20,981 |
| Year 1 cash flow (cumulative £35,000) | £35,000 |
| Year 2 cash flow (cumulative £75,000) | £40,000 |
| Year 3 cash flow (cumulative £117,000) | £42,000 |
| Year 4 cash flow (cumulative £155,000, payback reached partway through) | £38,000 |
| Payback period (years to recover £120,000) | approximately 3.08 years |
So what do these numbers actually tell you? The payback period of just over three years looks attractive on its own. But the NPV of £20,981 is the more important figure — it tells you that, after covering your true cost of finance, this machine is expected to add nearly £21,000 of value to your business in today’s money. Running the same cash flows through an internal rate of return calculation gives an IRR of approximately 17%. If your business borrows at, say, 8%, then a project returning 17% has a healthy margin of safety built in, and the case for buying the machine is strong on all three measures, not just the one your supplier likes to quote.
Payback period and IRR both have blind spots. Payback ignores everything that happens after the cash is recovered, so it can favour a machine that pays back quickly but delivers poor overall returns over one that takes longer to break even yet generates far more profit in total. IRR can also give misleading or multiple answers for projects with unusual cash flow patterns, such as a machine that requires a large second payment partway through its life for a major overhaul. When NPV and IRR appear to disagree, trust NPV — it directly measures the pounds of value the project is expected to add to your business, rather than expressing that value as a percentage.
Getting the Accounting Right
NPV, IRR and payback period help you decide whether to buy the machine — but once you have bought it, the accounting treatment is separate and follows normal financial reporting rules. The machine is a fixed asset, recorded on the balance sheet at cost, and then depreciated over its useful life so that the profit and loss account reflects a fair share of the cost each year, matching the income the machine helps generate. Assuming the machine is paid for in full by bank transfer and depreciated on a straight-line basis over its five-year life with no residual value, the bookkeeping looks like this.
| Account | Dr | Cr |
|---|---|---|
| Plant and machinery | £120,000 | |
| Bank | £120,000 |
Initial purchase of the packaging machine, paid in full by bank transfer on 1 January.
| Account | Dr | Cr |
|---|---|---|
| Depreciation expense | £24,000 | |
| Accumulated depreciation — plant and machinery | £24,000 |
Year one straight-line depreciation charge, based on a five-year useful life and no residual value (£120,000 divided by 5).
It is worth noting that the depreciation charge in your statutory accounts is not the same as the tax relief you actually receive. For UK tax purposes, most plant and machinery purchases qualify for capital allowances rather than depreciation, and many SMEs can claim the Annual Investment Allowance (AIA), which currently allows up to £1 million of qualifying expenditure to be deducted in full against taxable profits in the year of purchase. This can bring forward a significant corporation tax saving, improving the real cash return on the machine well beyond what the NPV and IRR figures alone suggest — so always check the current AIA limit and qualifying rules with your accountant before finalising the investment case.
What This Means for Your Business
- Never judge an investment on payback period alone — it tells you how quickly you recover your cash, not whether the investment is genuinely worth doing.
- Use NPV as your primary decision tool: if it is positive at your true cost of capital, the project is expected to add value to your business; if it is negative, the numbers say walk away, however good the payback looks.
- Cross-check NPV with IRR — if the IRR sits comfortably above your cost of borrowing or required return, that is a second, independent vote of confidence in the same decision.
- Before signing the purchase order, ask your accountant whether the machine qualifies for the Annual Investment Allowance, since accelerated tax relief can materially improve the real-world cash returns behind your calculations.
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Our team helps SME owners and finance teams turn machine quotes and project proposals into clear, board-ready NPV, IRR and payback analysis, backed by proper accounting and tax treatment.
