What happens when CPF SA reach full retirement sum of that year and you are not 55?

Once you hit FRS, you will no longer be allowed to do RSTU and OA to SA transfers. Mandatory contributions will still go into SA depending on allocation rate determined by your age band. If you achieve FRS at a very young age, and continue to let mandatory contributions + interest flow into SA, it should be possible to exceed ERS (will also depend on the rate of increase for the Retirement Sums set out in the preceding years till you reach age 55).​​​

Hi anon,

That is correct. You are not allowed to top up via RSTU if you have hit FRS. Mandatory contributions and VC are seperate from RSTU and will still carry on, with the annual limit being $37740 and the amounts being split amongst 3 accounts in the ratio that is relevant for your age band. (Unless you direct VC to MA, that's another issue altogether, and this does also impact your Annual Limit)

Yes, a very high CPF balance is possible in SA and OA as compounding works very well, and excess interest from MA (when BHS is reached) will spill to OA and add on. Your understanding is correct.

Mandatory contributions will grow your balance, but whether you will hit ERS before 55 depends on a number of factors such as how much you contributed, and your age.

At $181K (this year's FRS), the interest of $7K -ish is more than the increase of the FRS, and we haven't counted the extra 1% from OA (first $20K) as well as your mandatory contributions. It's very possible to hit ERS before 55 given enough time.