£11,310 of tax-free pay this year

What each part means

The number 1131 means you get £11,310 to £11,319 of tax-free pay in the year, which is £943.25 a month or £217.67 a week. Multiply the number by 10 to get the rough annual amount.
This is lower than the standard 1257, so HMRC has taken about £1,260 off your allowance. Common reasons are a State Pension, a company car or medical insurance, untaxed interest, rental income, or tax owed from a previous year. Your coding notice (P2) lists exactly what.
The letter N means you have transferred 10% of your Personal Allowance to your spouse or civil partner under Marriage Allowance.

Per year

£11,319

Per month

£943.25

Per week

£217.67

Everything you earn above this is taxed at the normal rates. On a cumulative code, unused allowance from earlier months carries forward.

Lower than the standard allowance, so HMRC is collecting tax on something else through this code.

Your P2 coding notice lists exactly what has been taken off. Use the coding notice breakdown below to check the arithmetic line by line.
The most common reason for a much lower code is a State Pension. If that is you, our State Pension page explains why it works this way.
Underpayments from earlier years are grossed up, so the figure on the notice looks bigger than the tax you actually owe.

1
Sign in to your Personal Tax Account. Under PAYE you can see what HMRC thinks you earn from each source and what is in your code, and you can correct most of it yourself.
Personal Tax Account (GOV.UK)
2
If you would rather talk to someone, ring the Income Tax helpline on 0300 200 3300 with your National Insurance number to hand. Ask them to explain each line of your code and to send you a P2 if you have not had one.
Income Tax enquiries (GOV.UK)
3
Once HMRC changes your code they send the new one to your employer or pension provider. Any tax you overpaid earlier in the year comes back automatically in your next pay on a cumulative code.