How do tax on savings work?

[Newtom]

Forgive my ignorance but have never had enough money for this to be an issue.

If I have 40k in savings. What do I actually pay tax on?
If I put 20k in and isa and 20k in a savings account for example with 6 percent. Would I only pay tax on the 6 percent interest on the savings account ? The isa would be tax free?

What if I save all of the 40k in the 6 percent account. Would I pay tax on it all the interest?

I have a job with basic rate tax. How does it all work?

Not any more. Most pay interest gross now because of the PSA.

ISA interest is tax free.

You can also earn up to £500 (higher rate taxpayer) or £1000 (basic rate taxpayer) in interest on other accounts tax free. This is the PSA or Personal Savings Allowance.

If you go over the PSA, HMRC should adjust your tax code. You don't have to do a tax return just for this.

www.thetimes.co.uk/money-mentor/banking-saving/personal-savings-allowance#:~:text=If%20the%20interest%20you%20earn,earn%20in%20the%20tax%20year.