The formula
How to calculate p/E ratio
The price/earnings ratio is what the market is paying for each pound of annual profit. A P/E of 14 means fourteen years of current earnings would repay the share price — a rough, useful way to read what a valuation implies.
Earnings yield, the reciprocal, is often the more intuitive form. It puts a share on the same scale as a bond yield or a savings rate, which makes the comparison between asset classes direct.
What to enter:
- Share price
- Earnings per share
Results appear immediately — there is nothing to submit. Changing a field rewrites the link, so you can share the exact scenario you are looking at.
The order the fields are filled in makes no difference to the result — the calculator recomputes the whole formula from whatever is currently in every field, not step by step. That means it is safe to adjust one number, watch the result change, and adjust it back, without worrying about resetting anything first.
Why p/E ratio matters
A calculation like this usually gets used at a decision point rather than out of curiosity — comparing two real options, checking a number a lender or adviser has quoted, or working out whether a plan that sounded fine in conversation still holds up once it is written down with actual figures. The maths itself is rarely complicated; what is hard is remembering which figures to use and in what order, which is exactly what a dedicated calculator is for.
This tends to come up when comparing two concrete alternatives — two lenders, two savings products, two ways of structuring the same decision — rather than in the abstract. Run both scenarios through the same calculator with the same assumptions and the comparison becomes fair, because the only thing changing between the two results is the number you are actually trying to test.
It is also worth being clear about what a single figure like this can and cannot settle on its own. It answers the specific question the formula was built to answer, and nothing more — a favourable p/E ratio result does not automatically mean a decision is a good one overall, since plenty of other factors that a formula cannot capture, from personal circumstances to how comfortable a commitment feels, usually matter just as much as the arithmetic. Use the number as one solid input among several rather than the whole of the decision.
In practice, most people arrive at a page like this one having already tried a version of the calculation by hand or in a spreadsheet, and use the calculator here to confirm it rather than replace it. That is a reasonable way to use it — the two should agree to the last decimal place if the same inputs and the same formula are used, and if they do not, the formula shown above is the one to check your own working against first.
Worked example
Work through the defaults on this page:
- Share price: 42
- Earnings per share: 3
That gives:
- P/E ratio: 14 ×
- Earnings yield: 7.14 %
- Years of earnings to repay the price: 14 years
These figures are only the calculator's own starting values, included so the working is visible rather than hidden inside the tool above. Replace them with your own numbers and the same arithmetic applies — nothing about the method changes, only the inputs feeding it.
Reading the result
A high P/E is a statement about expected growth, not about quality. It only pays off if the growth arrives. Compare against the same company's history and its sector — a 25× software company and a 25× utility are telling you very different things.
Where this goes wrong. Comparing across cycles. A cyclical business looks cheapest at the top, when earnings are peaking, and most expensive at the bottom. For those, a cyclically adjusted ratio using average earnings over ten years is far more informative.
A useful check on any unfamiliar result is to compare it against a rough mental estimate first — round the inputs to convenient numbers and see whether the calculator's answer lands in roughly the same territory. A wildly different figure usually means one of the fields was entered in the wrong unit, most often a percentage typed as a whole number where a decimal was expected, or the reverse.
There is no universal figure. Broad developed markets have averaged somewhere in the mid-teens over long periods; below that suggests low expectations, above it suggests high ones. The question worth asking is what growth the price implies and whether it is plausible.
Trailing uses the last twelve months of reported earnings — factual, but backwards-looking. Forward uses analyst estimates for the year ahead, which is more relevant and more often wrong.
The answer it gives you is p/E ratio. With 42 share price and 3 earnings per share, that comes to 14 ×. Change any field and the figure moves with it.
Whenever one of the underlying figures changes — a new interest rate, a different balance, an updated term — since the result only reflects what is currently in the fields. There is no need to keep a separate record of past results; the web address for a filled-in version already carries the figures used to produce it.
Not unless a tax rate or a fee is explicitly one of the inputs above. Where it is not, the figure shown is a gross calculation, and any tax due depends on your personal circumstances and current tax rules, which are worth checking separately.
The arithmetic itself is exact — the calculator applies the formula shown above precisely, with no rounding until the final figure is displayed. The uncertainty, where it exists, is entirely in the inputs: an estimated rate or an approximate balance carries that same approximation through to the result.