The formula
How to calculate sick pay
Statutory sick pay is a flat weekly amount, paid for up to 28 weeks after the first three qualifying days. It is far below most people's normal earnings, which is what makes the shortfall figure the important one.
The first three days are waiting days and are unpaid unless a company scheme covers them or you were recently off sick. SSP requires average weekly earnings above the lower earnings limit.
Here is what each field means:
- Statutory sick pay per week — the 2025/26 rate; it changes each April
- Weeks off sick (weeks)
- Normal weekly pay
- Company sick pay (% of normal pay) — set to 100 for full pay, 50 for half pay, 0 for SSP only
The result updates on every keystroke. The URL updates too, which makes the filled-in version easy to bookmark or send to someone else.
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 sick pay 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.
The reason a page like this exists at all, rather than leaving the calculation to a spreadsheet or a textbook appendix, is that the formula behind sick pay is fiddly enough to get wrong by hand but not complicated enough to need specialist software. That middle ground — real enough maths to matter, simple enough to check instantly — is exactly what a dedicated calculator is for, and it is why the same figure recalculated here should match a careful manual calculation almost exactly.
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
Here is the calculation with the starting values:
- Statutory sick pay per week: 118.75
- Weeks off sick: 6 weeks
- Normal weekly pay: 620
- Company sick pay: 0 % of normal pay
That gives:
- Total sick pay: 712.5
- Per week: 118.75
- Shortfall against normal pay: 3,007.5
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
The shortfall is the case for income protection insurance. Six weeks off on SSP alone costs around £3,000 for someone earning £620 a week, against a household budget that has not changed.
Where this goes wrong. Company sick pay schemes usually taper — full pay for a period, then half pay, then SSP only. Model each stage separately rather than assuming one rate throughout.
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.
Up to 28 weeks in any one period of sickness. After that, Employment and Support Allowance or Universal Credit may be available instead.
Not for the first seven days, which can be self-certified. Beyond that an employer can require a fit note from a GP or other approved healthcare professional.
It returns total sick pay. With 118.75 statutory sick pay per week, 6 weeks weeks off sick and 620 normal weekly pay, that comes to 712.5. 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.