Most practices know the individual deadlines by heart. What's less often mapped out is how they stack — which months carry genuine overlapping peaks, and which are comparatively quiet. That shape is what actually drives capacity planning, not any single date in isolation.
| Deadline | What's due |
|---|---|
| 31 January | Self Assessment online filing and balancing payment; first payment on account |
| 5 April | End of the UK tax year |
| 6 April | Start of the new UK tax year |
| 31 May | P60s issued to employees for the previous tax year |
| 6 July | P11D and P11D(b) submission deadline for the previous tax year |
| 22 July | Class 1A National Insurance payment on benefits (19 July if paying by post) |
| 31 July | Second Self Assessment payment on account |
| 5 October | Deadline to register for Self Assessment for the previous tax year |
Several major deadlines aren't fixed calendar dates — they're set relative to each client's own year end or VAT stagger group, which is exactly why they're easy to underestimate at a practice level:
For a practice with a typical UK client mix, the two genuinely heavy periods are:
With MTD for Income Tax now live for higher-income sole traders and landlords, a third, smaller pattern is emerging: quarterly update deadlines in August, November, February and May adding a steady drumbeat on top of the existing calendar, rather than one big annual spike (see our MTD for Income Tax guide for the detail).
Deadline-driven workload is predictable a year in advance — the dates don't move. The practices that manage capacity well aren't the ones with the most staff; they're the ones who've mapped their actual client mix against this calendar and know exactly which weeks need more hands, rather than discovering it each time a peak arrives.