You will build a worksheet that allocates a monthly salary across accounts and estimates a year's interest.
Kelvin wanted one number before he made any CPF decision: how much his accounts would grow this year if he did nothing. His statement could tell him what happened last year, but not what next year would look like with his new salary. So he built a small worksheet. It took him about half an hour, and he now updates it every January.
This exercise walks you through the same build. You need a spreadsheet, your latest CPF balances, and the current tables from cpf.gov.sg: contribution rates, allocation rates for your age band, the Ordinary Wage ceiling, interest rates and the extra interest rules. Every rate in the worked example below is made up. Replace each one with the current figure before you trust a result.
Put every figure you might change in its own cell at the top of the sheet, with a label beside it. That way, when the CPF Board revises a rate next year, you change one cell and the whole sheet updates.
Your inputs are your monthly salary, your age, the Ordinary Wage ceiling, the total contribution rate for your age, the three allocation rates for your age (the share of wages going to the OA, SA and MediSave), your opening balance in each account, the interest rate for each account, and the extra interest rules. The CPF allocation table gives each account's share as a percentage of wages, so copy it that way.
Kelvin's inputs, with example figures: salary S$5,800, age 32, a made-up total contribution rate of 35%, split as 21% to the OA, 6% to the SA and 8% to MediSave. His opening balances are S$40,000 in the OA, S$15,000 in the SA and S$25,000 in MediSave. For interest he uses example rates of 3% for the OA and 5% for the SA and MediSave, which are not the current CPF rates.
Contributions are only charged on wages up to the Ordinary Wage ceiling, so the sheet should never multiply your full salary by the rate. Add a cell for wages subject to CPF, using a formula like =MIN(salary, ceiling). If you earn above the ceiling, this is the step that stops the sheet from overstating your contributions.
Kelvin earns below the ceiling, so his full S$5,800 counts. A colleague earning well above it would see the same contribution as someone earning exactly the ceiling. Bonuses are treated separately as additional wages, with their own yearly ceiling. If you get a regular bonus, add it as a separate row and look up how the Additional Wage ceiling applies.
Now multiply the wages subject to CPF by each rate. Kelvin's total monthly contribution is S$5,800 times 35%, which is S$2,030. Of that, S$1,218 goes to the OA, S$348 to the SA and S$464 to MediSave. Add the three as a check: S$1,218 plus S$348 plus S$464 is S$2,030, which matches.
Multiply each by 12 for the year. Kelvin's contributions come to S$24,360: S$14,616 to the OA, S$4,176 to the SA and S$5,568 to MediSave. If your MediSave is close to the Basic Healthcare Sum, cap the MediSave line at the room left and move the rest to the account it overflows to, as lesson 1.3 explained.
Interest has three parts, so give each its own row.
Interest on the opening balance: opening balance times the account's rate. For Kelvin that is S$1,200 on the OA, S$750 on the SA and S$1,250 on MediSave. Interest on new contributions: each month's contribution starts earning the month after it arrives, as lesson 1.2 explained. If a contribution arrives in every month from January to December, the months they earn add up to 66. So multiply the monthly contribution by 66, then by the rate, then divide by 12. For Kelvin that gives about S$200.97 on the OA, S$95.70 on the SA and S$127.60 on MediSave. Extra interest: work out how much of your combined balance qualifies under the current rules, remembering that only part of the OA can count, then multiply by the extra rate. To show the formula, Kelvin uses a made-up rule of an extra 0.5% on the first S$50,000, with no more than S$15,000 of OA counted. His qualifying balance is S$15,000 of OA plus S$15,000 of SA plus S$25,000 of MediSave, which is S$55,000, capped at S$50,000. His extra interest is S$250.
Add the rows. Kelvin's estimate for the year is S$3,874.27. Round it to S$3,870 when you write it down, because the inputs are estimates.
A worksheet you have never tested is a guess. Copy the sheet into a second tab, put in last year's opening balances, last year's salary and last year's rates, and compare the interest it predicts with the interest credited on last year's CPF statement.
Kelvin's test tab predicted S$3,640, using last year's figures, and his statement showed S$3,580 of interest in total. The gap was under 2%, and he could explain it: one month's contribution arrived late after a payroll change, and he had paid a course fee from his OA in March. A gap of a few percent is fine. A large gap usually means a wrong rate, a missed withdrawal, or extra interest counted on more of the OA than the rules allow.
Yours is done when it has labelled input cells with this year's CPF Board figures, a wage line that applies the ceiling, monthly and yearly contributions for each account that add up to the total, three interest rows for each account, and a test tab that comes within a few percent of last year's statement. Note the date you copied the rates beside the inputs, so you know when they need refreshing.
Use your own salary, age and balances, and keep last year's statement open next to the sheet for the comparison.
Build the worksheet with your own salary and age, and compare its interest estimate with the interest on last year's CPF statement.
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