Would it be wise to top up my mum's CPF RA to allow her to receive a decent annuity from CPF Life until she passes on?

It depends on your family cashflow.

For general idea, CPF earns from 4% up to 6% interest (6% on the first 30k combined and 5% on the next 30k combined). So the best is top max out the extra interest first.

If your cashflow is really tight, suggest to top up $3,000 per year (since your mum will be able to take out $250 a month = $3,000) so that there is some earning of interest in there. Risk free 6% interest on $1,375.00 is interesting imho (about $82.50) of interest

Whether to choose CPF Life or not, i think its not for anyone to recommend until we know much more about the family finances and how to structure.

If we have to put a mathematical calculations, RSS will be better until age 90, where CPF LIFE will be better after age 90.

Hi Anon, to be placed on CPF Life, your mom would require a minimum of 60k in RA before 80, if not she'll be on the older RSS scheme.

So a 50k top up is an option to immediately earn 4% and then get about 4300/yr in CPF Life payouts from 65 on standard plan, or if she has a spouse, can consider doing a RA to RA transfer.