Very basic ISA transfer question

surferstar

I’ve never transferred an ISA before but one product term ends in a few weeks so I understand I need to transfer to another provider (which offers more interest) rather than withdrawing, to avoid losing the ISA allowance. 

My question is, when transferring, assuming you have the max £20k can you choose the amount to transfer? As with interest the balance is more like £21k. Would I transfer £20k, leave £1k in there and withdraw that £1k?

The interest takes you above the £20k tax free amount so I’m a bit confused how it works and what to do with the excess without making a mistake and losing any allowance or tax free benefits. 

Albermarle

The £20K limit is only for new money added each tax year. You can transfer any amount you like that was added in previous tax years , including interest gained.

If you read through this forum, it is a good way to be better informed about ISA rules. For example.
ISA rules — MoneySavingExpert Forum

slinger2

When transferring a Cash ISA you can either transfer the whole amount (including interest) or do a partial transfer, where you specify the sum to be transferred. If you're thinking of a partial transfer be aware that not all providers support this option. Read the small print.