The rule
HMRC's technical notes give every date column the format yyyy-mm-dd, for example 2025-09-30 for 30 September 2025.
Why dates go wrong
- Spreadsheets show dates in your computer's format, such as 30/09/2025, and may save them that way.
- Files from US based tools use month first, such as 09/30/2025.
- Some exports hold dates as numbers, such as 45930.
What the checker does
It reads day first dates by default (you can switch to month first), dates written with month names and spreadsheet date numbers, and writes them all as yyyy-mm-dd. Dates that do not exist, such as 31 February, are flagged. It also warns when an event date falls outside the tax year you chose.
Based on HMRC's published guidance: EMI technical note. Checked on 20 October 2026. This is general guidance, not tax advice, and HMRC's own pages take priority if they change. Share Scheme Return is not affiliated with HMRC.
Let the free checker find these for you
Load your option register or finished return and see every row HMRC is likely to reject, with the reason and the fix. Nothing is uploaded, and you don't need an account.