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Expiry Date & Shelf Life Calculator

Calculate product expiration date, remaining shelf life days, and best-before window from manufacturing date.

months
Expiry date
Monday, 31 January 2028
Time remaining
537 days
Shelf life used
26.4%
730 day shelf life

How this is calculated

2026-01-31 + 24 months = Monday, 31 January 2028

Adding calendar months clamps to the last valid day of the target month. A product made on 31 January with one month of shelf life expires on 28 February, not on 3 March — which is what naive month arithmetic produces.

Expiry Date & Shelf Life Calculator: how it works

Adding months to a date is not the same as adding days, and getting it wrong produces expiry dates that fall in the wrong month entirely.

The month-end problem

A product manufactured on 31 January with one month of shelf life expires on 28 February — the last day of the target month. There is no 31 February to land on.

The correct behaviour is to clamp to the last valid day of the target month: 28 February, or 29 in a leap year.

Worked examples

ManufacturedShelf lifeCorrect expiryNaive result
31 Jan 20261 month28 Feb 20263 Mar 2026
31 Jan 20241 month29 Feb 20242 Mar 2024
31 Aug 20256 months28 Feb 20263 Mar 2026
15 Jun 202624 months15 Jun 202815 Jun 2028

How expiry is actually printed

  • Medicines usually print month and year only, and are valid to the last day of that month.
  • Food often prints a specific date, and "best before" differs from "use by" — the first is quality, the second is safety.
  • Cosmetics may print a period-after-opening symbol, a jar icon with a number of months, which starts from first use rather than manufacture.

Frequently asked questions

Add the shelf life in months to the manufacturing date, clamping to the last valid day of the target month where the original day does not exist in it.

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