The ISA allowance for the 2023/24 tax year is £20,000. You can, however, add money to your ISA until 23:59 on the 5th of April each year, as the allowance doesn’t carry over. ✔
Note: Deposits made via certain payment methods may take longer to reflect in your ISA. Should you prefer to deposit near the end of the tax year, the execution time of the transaction needs to be considered.
If you wish to learn more about ISAs, you can check our 'Trading 212 Learn' article on the topic.