You will build a shared cost sheet that calculates each partner's monthly contribution.
By now you have done the split once on paper in lesson 3.1, sorted your costs into shared, personal and to be discussed in lesson 3.2, and listed the unpaid work in your home in lesson 3.3. On paper, though, a split has to be redone every time a bill or a salary changes, and couples usually get tired of redoing it after the second time.
This exercise turns it into a small spreadsheet that does the arithmetic for you. Google Sheets, Excel or Numbers all work. Use one you can both open, because the point is that either of you can update it.
At the top of a new sheet, make an inputs block. In one cell write your take-home pay and in the cell below it your partner's. Use the average of the last few payslips if either income moves around, and note beside it which method you used, such as "base pay only" or "12-month average".
Below that, list every shared cost from lesson 3.2, one per row, with its monthly amount. For costs that come once or twice a year, such as conservancy charges paid quarterly, property tax, or the Chinese New Year red packet budget, divide the yearly total by twelve. Add a total row at the bottom that sums the column.
Next to the inputs, make a small results table with two columns, Equal and Proportional, and rows for each partner.
For the equal split, each partner's amount is the total shared costs divided by two.
For the proportional split, first work out each partner's share of combined pay: their take-home divided by the sum of both take-home figures. Then multiply the total shared costs by that share. If your pay is in cell B1, your partner's in B2 and the total shared costs in B12, your proportional amount is =B12*B1/(B1+B2).
Add two more rows: what each partner has left after paying their share under each method. That is their take-home minus their share. These are the rows you will actually talk about.
Under the table, write the method you agree on, in words, with the date. Then add any adjustment for unpaid work or uneven obligations that you discussed in lesson 3.3: a monthly top-up to one partner's personal savings, a cost the higher earner covers alone, or an agreement to rerun the sheet when hours change. If an adjustment involves money, give it its own row so the sheet shows the final monthly amount for each person, not just the split.
The final figure for each partner is what their standing transfer into the shared account from lesson 2.4 should be. Open your banking apps and change the amounts now. A sheet that says one thing while the bank sends another is worse than no sheet, because both of you will trust the wrong number.
Hui Min and Daniel's figures are examples. Their inputs are take-home pay of S$6,000 for Daniel, using his 12-month average including commission, and S$4,000 for Hui Min. Their shared costs are rent S$1,700, utilities and internet S$200, groceries and household S$700, and the BTO flat fund S$400. The total is S$3,000.
Their results table shows:
Under the equal split, each pays S$1,500. Daniel keeps S$4,500 and Hui Min keeps S$2,500.
Under the proportional split, Daniel's share of combined pay is 60%. He pays S$1,800 and keeps S$4,200. Hui Min pays S$1,200 and keeps S$2,800.
They choose proportional and write: "Proportional on take-home, Daniel on 12-month average. Agreed in March." They add one adjustment row, which currently reads zero: "If either of us cuts paid hours, rerun this sheet within a month and agree a top-up for that partner's own savings or CPF."
Then they update their standing transfers into Shared. Daniel's moves from S$1,500 to S$1,800, and Hui Min's from S$1,500 to S$1,200. The shared account still receives S$3,000 a month, and Hui Min keeps S$300 more of her own pay.
That is what done looks like: a sheet you can both open, with both splits side by side, the "left over" line for each method, your chosen method and any adjustments written in words with a date, and standing transfers that match the sheet to the dollar.
Sit down together with both payslips and your list of shared costs from lesson 3.2, open a blank sheet and start with the inputs block.
Complete the split calculator, agree the method, and update your standing transfers to match.
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