Every UK employer that provides company cars must report the benefit to HMRC. For the 2025/26 and 2026/27 tax years that still means filing a P11D for each affected employee, paying Class 1A National Insurance, and meeting strict deadlines. Get any of it wrong and HMRC can open a compliance check, issue penalties, and leave employees on incorrect tax codes.
This guide covers exactly what goes on the P11D for a company car, the key dates, the employer P11D(b) return, and what happens when mandatory payrolling replaces most P11D reporting from April 2027.
What Goes on the P11D for a Company Car
The P11D (Expenses and Benefits) form tells HMRC the taxable value of every benefit you provide to each employee. For company cars you need to report the following on Section F of the form:
P11D value — the car’s original list price on the day it was first registered, including manufacturer-fitted options and accessories plus VAT. This is not the price you paid or the lease cost; it is always the full UK retail list price. First registration fee and Vehicle Excise Duty are excluded.
CO2 emissions and fuel type — HMRC uses WLTP-measured CO2 figures (for cars registered from 6 April 2020) to look up the correct BIK percentage. Record the exact g/km figure from the V5C registration document and whether the car is petrol, diesel, hybrid, or fully electric.
BIK percentage — the percentage that applies based on the car’s CO2 band for the relevant tax year. For 2026/27, fully electric cars attract 3%, rising to 4% in 2027/28, while a typical petrol car at 120 g/km attracts around 30%.
Dates the car was available — if the car was first made available part-way through the tax year, or was returned before 5 April, the BIK is pro-rated. Report the exact dates so HMRC can calculate accordingly.
Private fuel — if you paid for any fuel used for private journeys during the year, you must report the fuel benefit separately. Even a single litre of private fuel triggers the full fuel benefit charge, which for 2026/27 uses a multiplier of £29,200.
P11D Deadlines for 2025/26 and 2026/27
The annual P11D cycle follows the same timetable each year. For employers still filing P11D forms (rather than payrolling), the deadlines that matter are:
- 6 July 2026 — submit P11D and P11D(b) forms to HMRC for the 2025/26 tax year. You must also give a copy of the P11D to each employee by this date.
- 19 July 2026 — deadline for Class 1A NIC payment by cheque.
- 22 July 2026 — deadline for Class 1A NIC payment made electronically (the date most employers use).
- 6 July 2027 — P11D and P11D(b) filing deadline for the 2026/27 tax year.
- 22 July 2027 — electronic Class 1A NIC payment deadline for 2026/27.
Missing the 6 July filing deadline triggers automatic penalties of £100 per 50 employees for each month (or part month) the return is late. Late payment of Class 1A NIC attracts interest from day one at HMRC’s prevailing rate, currently around 7.5%.
HMRC now requires P11D and P11D(b) forms to be filed electronically through PAYE Online for Employers, PAYE Online for Agents, or recognised payroll software. Paper returns are no longer accepted.
Calculating Class 1A NIC on Company Cars
Employers owe Class 1A National Insurance on every benefit in kind reported on P11D forms. The rate for 2026/27 remains 13.8% of the total taxable benefit value.
The formula for a single company car is straightforward:
P11D value x BIK percentage = taxable benefit Taxable benefit x 13.8% = Class 1A NIC
For example, take a petrol company car with a P11D value of £38,000 and a BIK rate of 30%:
- Taxable benefit: £38,000 x 30% = £11,400
- Class 1A NIC: £11,400 x 13.8% = £1,573.20 per year
If the same employee also receives private fuel, you add the fuel benefit charge (£29,200 x 30% = £8,760) and pay Class 1A NIC on that too — an additional £1,208.88. For larger fleets these figures add up fast, which is one reason many employers are switching to electric vehicles where the 3% BIK rate cuts both employee tax and employer NIC.
Tripbook helps fleet managers maintain accurate mileage records that distinguish business and private journeys — data that feeds directly into P11D reporting.
The P11D(b): Employer Declaration and Class 1A NIC Return
Alongside individual P11D forms for each employee, every employer must file a P11D(b) — the return that declares the total value of all benefits provided and confirms the Class 1A NIC liability for the year.
Key points about the P11D(b):
- It must be filed by 6 July, the same deadline as individual P11Ds.
- Even if you have no employees with benefits, you must submit a nil P11D(b) to confirm this.
- If you are payrolling benefits voluntarily, you still need to file a P11D(b) to declare Class 1A NIC on the payrolled amounts. Individual P11Ds are not required for payrolled benefits, but the P11D(b) is.
- From April 2027 under mandatory payrolling, Class 1A NIC will be reported and paid in real time through RTI, and the P11D(b) requirement will fall away for most benefits.
The P11D(b) is the document HMRC uses to collect payment, so errors here directly affect how much you owe. Cross-check it against your individual P11Ds before submitting.
Common P11D Errors That Trigger HMRC Enquiries
HMRC’s compliance teams look for patterns in P11D data. These mistakes most frequently lead to enquiries:
Wrong P11D value — using the discounted purchase price or lease cost instead of the manufacturer’s full list price. Dealer-negotiated discounts are irrelevant; the P11D value is always the published list price.
Incorrect CO2 figure — cars registered before 6 April 2020 may use NEDC figures, while those registered after use WLTP. Mixing the two standards shifts the BIK band and changes the tax liability.
Omitting manufacturer accessories — factory-fitted options must be included in the P11D value. Dealer-fitted accessories added after registration are treated separately and only included if they cost over £100.
Wrong availability dates — the benefit runs from the date the car is first made available, not the date the employee starts driving it. It ends on the date the car is returned or employment ceases, whichever is earlier.
Forgetting the fuel benefit — if private fuel was provided at any point during the year and not formally withdrawn, the full annual fuel benefit charge applies with no pro-rating.
The Move to Mandatory Payrolling from April 2027
The biggest change to P11D reporting in decades arrives on 6 April 2027, when mandatory payrolling of benefits in kind takes effect. Originally planned for April 2026, HMRC delayed the start date to give employers, payroll software providers, and agents more time to prepare.
Here is what changes:
- From 2027/28, the taxable value of most benefits (including company cars) will be reported through Full Payment Submissions (FPS) each pay period, and income tax will be collected through PAYE in real time.
- Class 1A NIC will also be processed monthly through the payroll, rather than as a single annual payment after filing P11Ds.
- Individual P11D forms and the P11D(b) will no longer be required for most benefits. The exceptions are beneficial loans and living accommodation, which remain on P11D for now.
- HMRC has confirmed a “soft landing” for 2027/28 — no penalties for accidental errors in the first year unless there is deliberate non-compliance.
For 2026/27 (the transitional year): employers who registered for voluntary payrolling before 5 April 2026 can payroll company car benefits during 2026/27. A P11D(b) is still required for that year, and the final P11D/P11D(b) filing deadline of 6 July 2027 still applies. Employers who did not register in time must continue filing P11Ds as normal for 2026/27.
Be aware of the potential “double tax” overlap when switching: employees may temporarily pay tax through both their adjusted tax code (from the previous year’s P11D) and the current month’s payrolled amount. Communicate the change to affected employees early.
For a detailed breakdown, see our guide on payrolling benefits in kind from 2027.
Keeping Accurate Records for P11D
HMRC expects employers to maintain records that support every figure on the P11D. For company cars, keep:
- V5C documents confirming make, model, CO2, and fuel type for each vehicle
- The manufacturer’s confirmed list price and factory-fitted options
- Dates each car was allocated to and returned by employees
- Records of private fuel provision, including start and end dates
- Details of accessories added after registration costing over £100
Retain these records for at least six years following the end of the tax year they relate to.
For employees tracking business mileage to support P11D data or claim mileage allowance payments, Tripbook provides automatic GPS-based mileage logging that captures every journey with date, distance, and route — exactly the detail HMRC expects.
Download Tripbook on the App Store to keep compliant mileage records alongside your company car.
For BIK rates and how they affect the figures on your P11D, see our company car BIK calculator. For more on how business mileage record keeping supports HMRC compliance, see our dedicated guide.
