What belongs in the calculation
HMRC’s detailed guidance says the function cost includes VAT and employer-provided transport or overnight accommodation. Divide that complete relevant cost by everyone who actually attends, including non-employees. Do not use the invitation list or employee count when the actual denominator is different.
Cost per head = complete relevant function cost ÷ total people who attend
Why the result is not a tax verdict
Current HMRC guidance also requires the function to be annual and generally available to employees, with separate rules for multiple annual functions and salary sacrifice. The £150 figure is an exemption threshold, not an amount to deduct from a higher result.
A figure at or below £150 can still fail another condition. A figure above it requires review of the full treatment rather than taxing only the excess. Keep the office party release checklist with the calculation.
Version and test status
Version 0.1, 7 September 2026. Zero-cost, exact-threshold, above-threshold, changing-attendance and multiple-function arithmetic are covered by automated checks. The tool deliberately does not decide whether an event qualifies, who is taxable, what must be reported or how payroll should treat it.
Questions people ask
How is office party cost per head calculated?
Divide the complete relevant function cost by everyone who actually attends, including non-employees. HMRC’s detailed guidance says relevant costs include VAT and employer-provided transport or overnight accommodation.
Is £150 per employee a tax-free allowance?
No. HMRC describes an exemption threshold with conditions; it is not an allowance to deduct from a higher cost. Use the actual attendee denominator and ask payroll or a tax professional to apply the current rules.
What happens if attendance drops?
Rerun the calculation using actual attendees. A committed £6,900 event is £138 per head for 50 attendees but approximately £156.82 for 44, so attendance evidence can change the arithmetic.
Do guests count in the attendee number?
HMRC’s detailed guidance says to divide by the total number of people who attend, including non-employees.
Do transport and accommodation count?
Employer-provided transport or overnight accommodation enabling attendance are included in HMRC’s detailed function-cost description, along with VAT.
How do multiple annual parties affect the result?
HMRC has separate rules for selecting annual functions whose combined cost per head stays within the threshold. Enter the per-head cost of other functions only as an arithmetic prompt and have payroll decide the actual selection and reporting treatment.
Sources and assumptions
- HMRC — expenses and benefits: social functions and parties — current annual, open-to-all, £150-per-person, multiple-function and salary-sacrifice conditions
- HMRC Employment Income Manual EIM21690 — updated 12 August 2026; cost definition, actual-attendee denominator, exemption-not-allowance boundary and multiple-function detail