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How to calculate percentage in Excel, and the format trap

There are two halves to how to calculate percentage in excel, and the pages answering it almost always give you one. The formulas are the easy half and they are below. The half that produces the wrong answers is the percentage format, which does something different depending on when you apply it — and Microsoft documents that, on a page ranked below three that do not mention it.

This is why a spreadsheet can show a figure that is wrong by a factor of a hundred and look entirely normal. Nothing is flagged. The cell has a value, the value has a per-cent sign, and the sign is doing exactly what it was asked. If a percentage in a sheet you did not build looks implausible, clicking the cell and reading the formula bar tells you in one second what the formatting is hiding.

The shortcut, and one reason to skip it. Ctrl+Shift+% applies the percentage format to the selection immediately, and Percent Style sits in the Number group on the Home tab. It is fast, and on a column that already contains numbers it is the exact keystroke that produces the multiply-by-100 behaviour above. Fast is fine once you know which of the two cases you are in.

Find, calculate or work out — and the word Microsoft uses. How to find percentage in excel and how to calculate percentage in excel are the same four formulas. Worth knowing which term the documentation uses, though, because it decides what you can look up: Microsoft calls the second calculation the percentage of change. Searching its help for percentage difference finds much less, and the arithmetic you almost certainly want is the change one — new minus old, divided by old.

Decimal places. The default format shows two, so a share comes out as 84.00% rather than 84%. Microsoft’s note is that Increase Decimal and Decrease Decimal change it. Worth using deliberately: two decimal places on a percentage calculated from small counts implies a precision the underlying numbers do not have — 42 out of 50 is not accurate to a hundredth of a per cent.

On percentage points. If a rate moves from 4% to 6%, that is a rise of two percentage points and an increase of fifty per cent, and both statements are true. Excel will happily compute either and cannot tell you which one your reader will assume. When the figure is going into a sentence somebody else reads, saying which of the two you mean costs three words and prevents the most common misreading of a number there is.

The formulas, the worked examples and both formatting behaviours above are quoted from Microsoft’s own Excel documentation, read on 22 August 2026 and listed below. The advice about decimal places and the note on percentage points are ours.

What this tower will not do

It will not give you the formulas and stop. The formulas are the half that works; the format is the half that produces wrong answers quietly.

It will not describe the percentage format as cosmetic. Microsoft documents two different behaviours for it, and both are quoted here.

And it will not confuse percentage points with per cent, or let a sentence do it by accident. What holds instead is simple: the formulas, the worked examples and both formatting behaviours are quoted from Microsoft’s own Excel documentation, with the date each page was read.