How is tax worked out?

[plum100]

I wonder if someone can explain it me so I can understand - I have googled it but can't seem to find the answer I am looking for.

I can earn £10000 before I pay tax. Normally I earn under that so all fine. However for a few months I have a lot of overtime booked - by the end of the year I wont have gone over my allowance as it will quieten down again and I will go back to my normal salary.

However I have been taxed this month, and I will be again in June. Is this because they look at that and think that if I earn this new figure every month I will go over my limit so they start to tax me right away? And if so does that mean I will get a rebate at the end of they tax year?

That would make sense to me but like I say I cant find the answer.

Thank you

It's cumulative.

If during month 1 of the tax year you earn under £833 you don't get taxed, month 2 your cumulative total is 1666 etc

If during the next few months your earnings drop under the cumulative level you'll get a tax refund.

The exception is if you are on a Week 1 tax code (usually if you've recently moved jobs).

However that isn't true of National Insurance contributions. If you go over the monthly limit for NI you don't get a rebate.