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Is topping up CPF SA worth it in my 20s, or invest instead?
The tax relief angle is underrated. If you're earning enough to pay meaningful income tax, the RSTU top-up gives you an immediate guaranteed "return" in tax saved on top of the 4%. But if your income is low and you pay little/no tax, that benefit is small and the illiquidity till 55 is a big cost at 26. So it partly depends on your tax bracket. Do the math on your actual tax saved before deciding.
9First-hand experience