If you are transferring funds into a Cash ISA (Easy Access), you will start earning interest from the day your funds settle in your account.
If you're transferring your balance from another provider, once the money is applied to your balance, you'll start earning interest. This means any gap in earning interest is usually limited only to the time it takes for the electronic transfer to clear between banks.
Fixed Rate ISAs operate a little differently because they involve locking your money away for a set period to secure a specific rate. For these accounts, you do not start earning interest the moment the funds land with us. Instead, interest begins to accrue only when your funds are fully allocated with our banking partner.
There is often a short window between us receiving your transfer and the funds being officially allocated to the fixed-term bond. During this brief processing period, interest is not payable.