Six lines on a UK 2026-27 P11D(b) are still being typed from last year's table, and on a single £42,000 electric company car they add £136.08 of employer Class 1A that nobody budgeted for. The payroll manager reading a rate sheet written in 2024 sends that return to HMRC by 6 July 2027, and it is wrong before anyone checks it.
Two numbers moved, and they moved away from how most people remember them.
The first is the appropriate percentage for a zero-emission car. It sat at 2% from 2020-21 through 2024-25, went to 3% for 2025-26, and is 4% for 2026-27. HMRC's 480 Appendix 2 table for 2026-27 reads 4% at 0 g/km, then five electric-range bands for cars at 1 to 50 g/km (4% at 130 miles or more of electric range, then 7%, 10%, 14% and 16% as the range falls), then 17% at 51-54 g/km rising one point for every additional 5 g/km, capped at 37%.
The second is Class 1A National Insurance. The employer rate was 13.8% until 5 April 2025. From 6 April 2025 it is 15%, and it is 15% for 2026-27. Class 1A is the employer's charge on the taxable value of the benefit, and unlike secondary Class 1 on salary it is not reduced by the Employment Allowance.
Put both through one ordinary car. A £42,000 pure electric company car, driver on the 40% rate, available all year, no capital contribution:
- 2024-25 rates: 2% of £42,000 is £840, and 13.8% of £840 is £115.92 of employer Class 1A.
- 2026-27 rates: 4% of £42,000 is £1,680, and 15% of £1,680 is £252.00 of employer Class 1A.
That is £136.08 more on one car per year, or £756 across a three-year lease. The driver's tax moved too: £672 a year at 40% instead of £336.
The petrol and diesel side is where it gets quietly expensive. A 120 g/km petrol car at the same £42,000 list price sits at 31% for 2026-27 — 17% for the 51-54 band plus one point for each of the fourteen 5 g/km steps up to 120. That is a £13,020 cash equivalent and £1,953 of Class 1A. Make it a diesel that misses the RDE2 standard and the supplement is 4%, taking it to 35%, a £14,700 benefit and £2,205 of Class 1A. RDE2-certified diesels are exempt, and nothing pushes the percentage above the 37% cap.
Two reducers get dropped by hand. An employee capital contribution cuts the list price used in the calculation, but only up to £5,000: type £8,000 and only £5,000 counts. Days the car was genuinely unavailable pro-rate the benefit. The same £42,000 EV with a £5,000 contribution and 90 days unavailable gives a £1,115.07 cash equivalent and £167.26 of Class 1A, not £252.
Then the deadline. P11D and P11D(b) for 2026-27 are due by 6 July 2027, and the Class 1A must be paid by 22 July 2027. The late-filing penalty is not a flat £100: it is £100 per 50 employees, or part of 50, for each month or part month the return is late. Twelve employees is £100 a month. A hundred and twenty is £300 a month.
The extension takes ten figures about the car, the driver and the payroll, and returns the 2026-27 percentage, the cash equivalent, the driver's tax, Class 1A at 15%, the 2024-25 comparison, the three-year total and the monthly late-filing exposure — in a browser popup or a free web page, with nothing sent anywhere.
That is free, for as many cars as you like, no key and no locked answers. The $60 licence adds a different axis: it saves each car as a .csv working paper you keep, and reminds you 30, 14 and 1 days before the filing date. UK accountancy fee guides for 2026 put P11D benefits reporting at £30 to £75 per employee.
Check one car against the table before the return goes in. The percentage you half-remember is two years old.
Free in your browser (the same rules): https://getreadystack.com/tools/company-car-bik-class-1a-2026-27
Licence ($60, once, 7-day refund): https://buy.polar.sh/polar_cl_MyA9NtPdM7q9pxdv6nV4U0dylRe05HPDCKOFO3y3r66
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