How do I calculate compounded gains for transferring OA to SA

Can consider other methods to get tax reliefs in the future as well - such as SRS.

This is super complex.

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Your tax bracket may change over time so it may be difficult to calculate that. Taking your top up limit as $8000. And since it will be future tax relief you are talking about, I will fast forward the CPF contribution for the future at $8000 per month. In 2026, up to $8000 salary per month will attract employer and employee CPF contribution. That works out to be $8000 x 0.37=$2960. So from your salary, $2960 will be contributed per month. If you do not have 13th month or bonus, your annual CPF contribution will be $2960x 12 months = $35520.

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CPF annual limit is $37,740. $37,740 - $35,520= $2,220.

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This means that in future if your salary is at $8000 gross per month, you can top up $2,220. If your gross salary is $8,000 per month, that you roughly put you in the 7% tax bracket. If your tax relief is $8000, 7% of $8000 is $560 savings.

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Now if you transfer your OA into your SA, the calculation for the CPF interest is roughly like this.

$1000 x 0.04 x n month / 12 months

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e.g this is Feb 2024. Your contribution from work comes in on 3 Feb 2024. So that contribution will only start attracting interest starting from March. Effectively, they will only earn interest for 10 months.

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$1000 x 0.04 x 10 months / 12 months = $33.33 for the rest of the year. As I don't have the actual calculation by CPF. This is how I do it. If they do compound. Then it would be as follows:

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$1000 x 0.04 x 1 month / 12 months = $3.33.

the next month of the same amount,

$1033.33 x 0.04 x 1month / 12 months = $3.44. ......

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So you keep adding the interest in but because you are working there will be a new $1000 added in.

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To end it all, just transfer inside SA. When you reach current FRS, the interest generated per year will cover the next increase in Minimum Sum. When you reach close to $280knin SA, it gives you $12,000 per year.