Hi. Does it make sense for my mum to do voluntary top up to her cpf? She is hitting 55 this august. Mum earns little and does not have much savings and was asking if topping up to her cpf is more wise

Is her SA+OA balance near FRS ($186k this year) or BRS ($93k with property pledge)?

The thing is when she turns 55, her RA will be created with FRS from SA first, then OA if SA insufficient. Only after FRS (or BRS with property pledge) met then she can freely withdraw from remaining balance in SA/OA. The money in RA will continue to earn interests, but she will only receive CPF LIFE monthly payouts when she is 65 to 70.

You can help her by topping up her SA to FRS and you get to enjoy up to $7k tax relief.