What is the voluntary top-up limit to my three CPF accounts?

The maximum amount you can voluntarily top up is the difference between the CPF Annual Limit of $37,740 and the mandatory CPF contributions made for the calendar year. Do remember to consider your mandatory CPF contributions which you will be receiving for the calendar year, before making voluntary top-ups.

If the total mandatory CPF contributions and voluntary top-ups exceed the CPF Annual Limit in the calendar year, any excess voluntary top-ups will be refunded without interest.

https://www.cpf.gov.sg/member/faq/growing-your-savings/top-up-your-cpf-accounts-to-build-your-savings/what-is-the-voluntary-top-up-limit-to-my-three-cpf-accounts