Every budget starts as a set of guesses. Electric, about $120. Groceries, $600 should do it. Phone, roughly $100.
That's fine. You have to start somewhere, and a plan built on guesses is far better than no plan. The problem is that guesses tend to be optimistic, and they stay in the plan long after you have the information to fix them. Months later the budget still says groceries are $600, every month comes up a little short, and nobody can say exactly why.
The fix takes about three months and very little effort: record what actually came out, and once you have three real numbers, replace the guess.
Why guesses run low
It isn't carelessness. It's how memory works. You remember the typical bill, not the high ones. You remember the grocery shop, not the extra trip on Thursday for milk and the thing you forgot. You remember last year's price, not this year's.
So most plans aren't wrong by a lot in any one place. They're wrong by a little in many places, mostly in the same direction. That adds up.
The routine
1. Record the actual every time. When a bill goes out, note what it really was, not what you planned. For variable spending like groceries, note the month's total.
2. Leave the plan alone for now. Recording this month's actual is not the same as changing the plan. One high electric bill shouldn't rewrite the budget.
3. After three months, compare. For each item that's been different every month, take the average of the three actuals.
4. Replace the estimate. Put the average in the plan. Done, until something changes.
Three months is a good balance. One month is noise. Twelve months is too long to live with a plan you know is off.
A worked example
A made-up household set up their plan in June. By the end of September, they have three months of real numbers:
| Item | Estimate | Jul | Aug | Sep | Average | Monthly gap |
|---|---|---|---|---|---|---|
| Electric | $120 | $164 | $188 | $152 | $168 | +$48 |
| Phone | $100 | $112 | $112 | $112 | $112 | +$12 |
| Groceries | $600 | $660 | $720 | $690 | $690 | +$90 |
| Car insurance | $200 | $180 | $180 | $180 | $180 | −$20 |
| Net | +$130 |
The plan has been $130 a month too optimistic. Over a year, that's $1,560: money the household thought it had and didn't. That's the feeling of "we're doing everything right and still always short," expressed in one number.
Notice the car insurance. Estimates don't only run low. Fixing them sometimes hands money back.
Watch out for seasonal bills
The electric bill in the example covers July to September: air-conditioning months. Replace the estimate with $168 and the plan will be a little high in spring and autumn, then perhaps too low in a cold January.
For bills that swing with the seasons, there are a few reasonable approaches:
- Use a full year of history if your provider shows it, and plan the twelve-month average.
- Ask about level billing. Many utilities offer a plan that spreads the yearly cost evenly. Your provider can tell you whether they do.
- Accept some swing, and check the estimate again each season.
Three months works well for things that are fairly steady. For things that aren't, be a little more patient.
When one month is just weird
A month with a birthday party, a car repair or a holiday will throw the grocery or spending average. Don't let one unusual month set the plan for the next year. Either leave it out of the average, or, better, ask whether it's really a one-off. Birthdays happen every year. If "unusual" months keep turning up, that's a sinking fund waiting to be created.
Look at the whole month too
Item by item is one view. The other is the month as a whole: what you planned to send out in each pocket, against what actually went. A recap like this answers questions the line items can't, like whether everyday spending is creeping up across the board, or whether a bill was planned and simply never paid.
Spending a few minutes on it at the start of each month is enough. Look at what came out different, decide whether it's next month's new normal, and move on.
