You will build a spreadsheet that shows your average monthly spending by bucket and sub-category against your take-home pay.
Wei Ling has three months of tagged transactions from lesson 1.3. Right now they are a long column of numbers with labels. Her figures come from lessons 1.2 and 1.3 and are made up for teaching. Turning that column into one summary table takes about 35 minutes. The table answers three questions: what a normal month costs, how that cost splits across needs, wants and future you, and where your memory was furthest from the truth.
Do the steps in order. You need two things beside you: the tagged list from lesson 1.3 and the guess you wrote down at the end of lesson 1.1.
Take out the one-offs before you total anything. A one-off is a cost that will not come back next month, such as a wedding, a flight, a laptop or a medical bill. If you average them in, one expensive month makes every month look expensive. A budget built on those numbers feels loose until the next big cost arrives.
Filter your list for the lines marked as one-offs, move them to a separate tab and note the month of each. Wei Ling has one: S$450 in December for a wedding gift and an outfit. She moves it to a tab called "one-offs" and notes the month beside it. One-offs still matter. Many of them come back next year, and module 3 turns them into a monthly amount you can set aside.
Set up a table with your sub-categories down the side and the three months across the top. Each cell holds that sub-category's total for that month. A pivot table builds all of these totals at once. If you'd rather use a formula, SUMIFS adds up the amounts where both the sub-category and the month match, one cell at a time. Then add a fourth column with the three-month average.
Wei Ling's eating out comes to S$480, S$610 and S$470, an average of S$520. Her rent is S$950 in all three months. Her rides range from S$110 to S$190, with an average of S$150.
Before you move on, check that the table is complete. The sum of all three months in your table should equal the total of your tagged list minus the one-offs. If the two numbers don't match, a line has no sub-category or has a typo in its label, so find it before you go further.
Total the averages in each bucket: needs, wants and future you. Divide each bucket total by your lowest normal take-home pay from lesson 1.1 to get its share.
Wei Ling takes home S$3,800. Her needs come to S$2,160 a month, about 57% of her pay. Her wants are S$1,250, about 33%, and future you gets S$100, about 3%.
Now compare these shares with the rough thirds from lesson 1.1. The thirds are a quick test of shape, and you aren't meant to hit them. On Wei Ling's pay a third is about S$1,267. Her wants land almost exactly on a third. Her needs run well over, because she rents a room and supports her parents, and that squeezes future you down to a sliver. Needs running well over a third is common for people in that position. For Wei Ling, the thirds show that no single bucket has gone wild, and that needs take more than half her pay before she makes any choices. She decides what to do about her high needs in module 2.
Last, note any gap between your bucket total and your take-home pay. Wei Ling's buckets add up to S$3,510 (S$2,160 + S$1,250 + S$100), which leaves S$290 a month unaccounted for. Money outside the buckets didn't vanish. It either went to a one-off or sat in the account until a later seasonal cost came along. For Wei Ling, some of it paid for the December wedding, and the rest stayed in her account until February, when she spent it over Lunar New Year. Lesson 3.1 comes back to both the wedding and Lunar New Year when it deals with this S$290.
Add two more columns to the table: your guess for each sub-category from lesson 1.1, and the difference between that guess and the three-month average.
Wei Ling had guessed S$2,900 a month for everything except savings. The real figure, needs plus wants, is S$3,410, a gap of S$510. Her needs guess was within S$10 of the real figure. Needs guesses tend to be close because rent and bills don't change from month to month. Almost all of her gap was in wants. Her three biggest surprises were eating out at S$220 over her guess, delivery at S$140 over and rides at S$90 over.
The biggest surprises usually show up in categories made of many small payments, where each payment felt too minor to remember at the time. Mark your own three biggest surprises, because module 4 starts looking for money in exactly those small-payment categories.
When you finish, you have one tab with a short table. It shows each sub-category, its three monthly totals, its average, your guess and the difference, with the three bucket totals and their share of take-home pay underneath. A second tab lists the one-offs with their months. Wei Ling's finished picture, from her eating out average down to her bucket shares, fits on one screen.
Keep this file, because every module after this one uses it, starting with the budgeting methods in module 2.
Build the spending picture with a summary table by bucket and a column comparing your memory-based guess with the real average for each sub-category.
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