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Understanding your P800 Tax Calculation

What is a P800 Tax Calculation?

A P800 is a document produced by HMRC that shows your income, allowances and tax relief’s for the tax year. It will show a calculation of the total income tax you should have paid and compare it to the amount you actually paid. 

You will usually only receive a calculation when HMRC think that you haven’t paid the right amount of tax.

If you have made a tax rebate claim

If you have made a tax rebate claim, you will likely receive four tax calculations as part of this process (one for each year you have claimed).

If you receive more than one calculation, do not add them together to work out your total refund! The calculations are cumulative and the result from each year is automatically included in the following year’s calculation until you reach the final year.

Your total rebate for all years will be the amount shown on page 2 of the final calculation:


This final amount will already include the previous years. The amount from the prior year is shown on page 2 under “Adjustments” (check it for yourself and you will see the amount will equal the figure from the previous year).


Let’s say you have made a tax rebate claim for uniform and business mileage and are owed £100 for each of the last 4 years (i.e. £400 in total). The “Result” on your P800 calculations for each year would look something like this:

2016/17 – HMRC owes you £100
2017/18 – HMRC owes you £200 (£100 from this year + £100 from last year)
2018/19 – HMRC owes you £300 (£100 from this year + £200 from last year)
2019/20 – HMRC owes you £400 (£100 from this year + £300 from last year)

As you can see in the example above, the total rebate due is £400 as shown in the final calculation. If you were to add each calculation up, you would arrive at £1000, which as nice as it would be, is not what you are owed!

Checking Your P800

It’s important to carefully check your P800 in order to ensure its accuracy. You should ensure that the figures are correct in order to avoid paying an incorrect amount of tax. Here are the key numbers you should check:


This includes your income from wages, pensions, state benefits, savings interest and employee benefits. You should check this against your P60, P45 and P11D.

Your deductions

This shows any specific tax reliefs you have claimed which reduce the income on which you need to pay tax. Deductions will normally be shown under two categories:
Flat Rate Job Expenses – this usually refers to your uniform cleaning allowance.
Job expenses – this will normally be for milage allowances or professional subscriptions/fees (e.g. Unison, RCN, NMC etc).

Your allowances

Nearly everyone in the UK has a tax free personal allowance. The personal allowance is deducted from your income. For 2015/16 the allowance was £10,600.


This will normally include under or overpayments from previous years which have not yet been paid back. Married couples allowance will also be shown here.


This is the final amount of tax you are owed or need to pay back. It will include any amounts which have already been refunded to you during the year (for example through your wages).

If your P800 seems correct, you do not need to do anything. When due, refunds will usually be sent via cheque within 4 weeks of receiving a P800.

If you have underpaid tax

If you owe tax to HMRC and this amount does not exceed £3,000 HMRC will collect this in instalments over the forthcoming year (unless you make a voluntary payment or your income is less than your Personal Allowance). If you owe more than £3,000, information will be provided on how you should make repayment.

If you think your P800 is wrong

If have made a claim with us and want to discuss your P800, please get in touch. If you have not made a claim with us, please contact HMRC or leave a comment below and we’ll do our best to help!

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