Fixed versus variable expenses, and why the split decides your budget

A fixed expense is one that arrives at the same amount on the same schedule whether or not you think about it, rent, a car payment, insurance, a subscription. A variable expense changes with your decisions week to week, groceries, fuel, dining out, shopping. The split decides how you budget, because the two kinds are managed in opposite ways: a fixed expense is changed once, by a call or a cancellation, and then stays changed, while a variable expense is managed every week by a rule. Your fixed share also tells you how much of the month is decided before it begins, which for many households is more than half.

The three kinds, not two

The two-way split leaves out a third kind that behaves like both. Utilities, fuel, and a phone plan with overages are due on a schedule you cannot skip, but the amount moves with the season and with use. Call them semi-fixed: fixed in whether, variable in how much.

Budget the semi-fixed ones at their twelve-month average, since a winter gas bill and a summer one differ by a factor of two or more, and treat them as committed for pacing purposes: the money is leaving whether or not the amount is exact.

Why the split decides how you budget

Fixed expenses are where a single decision saves the most. A subscription cancelled once saves its price every month with no further effort; a bill renegotiated once repeats the saving for the length of the contract. Variable expenses cannot be cut that way. No single decision lowers next month's grocery bill; a rule applied every week does, and it has to keep being applied.

The fixed share also sets the room. If fixed and semi-fixed expenses take 60% of take-home pay, then 40% is the whole of what the month has decisions about, and a budget that spends its attention pacing the 40% while ignoring the 60% is watching the smaller number. The fixed share is where the budget's shape is set, usually once a year; the variable share is where it is run, every week.

Find your own split

1. Pull three months of transactions from every account, and set aside the transfers between your own accounts.
2. Mark each transaction fixed, semi-fixed, or variable. The test is whether the amount would be the same next month if you made no decisions: yes is fixed, yes but for a different amount is semi-fixed, no is variable.
3. Add up each kind and divide by three for the monthly figure.
4. Divide each by take-home pay for the share. The fixed plus semi-fixed share is your committed share; the rest is the room.

A worked example

Take-home pay is $4,200 a month.

Sixty percent of this household's month is committed before it starts. The decisions the month actually contains are about $1,480 of variable spending and whether the $200 transfer happens. A budget for this household should spend a line on each fixed item, so the shape is visible, and its weekly attention on groceries, dining, and shopping, where a rule can move the total.

What to do with each kind

• Fixed: audit twice a year. Read every fixed item and ask whether you would sign up for it again today at that price. Cancel the ones you would not, and call about the ones that have a retention department. Each change repeats itself every month afterward; see How to cut spending without a budget for the order.
• Semi-fixed: budget the average, watch the season. A budget line at the twelve-month average is over in winter and under in summer, and that is correct. Compare each bill with the same month last year rather than with last month.
• Variable: one rule per large category. A frequency rule, one shop a week or takeout twice a week, is what moves a variable category, and it is applied every week. Pace the variable share through the month against the room left after the committed share, not against the whole paycheck.

Common mistakes

• Budgeting the whole paycheck as if it were variable. Pacing $4,200 when only $1,480 has decisions in it makes the first week look fine and the last week look like failure.
• Treating a subscription as variable because it is small. Its size does not make it a decision; its schedule makes it fixed, and it is cut once or not at all.
• Budgeting utilities at last month's amount. A summer figure in a winter budget is over by half; the twelve-month average is the honest line.
• Auditing fixed expenses monthly. Nothing changes month to month, and the attention belongs on the variable share. Twice a year is enough.
• Counting the car payment as variable because fuel is. The payment is fixed, the fuel is semi-fixed, and they need different lines.

Common questions

Are groceries a fixed or a variable expense? Variable. The amount changes with what you buy and how often you shop, even though eating is not optional. Fixed describes the amount and schedule, not whether the expense is a need.

Is a car payment fixed if I could sell the car? Yes. Fixed means the amount arrives unchanged unless you make a specific decision, and selling the car is that decision. Until then the payment is the same every month, which is what makes it fixed.

What fixed share is too high? There is no single figure, but above about 60% of take-home pay, the month has little room and every irregular expense becomes debt. If the committed share is that high, the lever is a fixed item, housing, a vehicle, or debt, not the grocery bill.

Are savings fixed or variable? Treat the transfer as fixed, on payday, at a set amount, because a savings line that is variable is the one that gives way first. Its amount is a decision, but a decision made once, like a bill.

Where do annual bills go? They are fixed, at one twelfth of the annual amount each month, set aside so the bill is covered when it lands; see How to budget for bills that aren't monthly.

How Zypper handles this

Zypper finds the fixed and semi-fixed items for you. As transactions sync, it identifies recurring groups, subscriptions, bills, utilities, and loan payments, from the pattern of your actual charges, and a bill in a spending category counts as money already spoken for from the start of the month it is due, at its usual amount before the charge arrives. Turn on Hide recurring in the budget page's display settings and the summary shows only your discretionary, non-recurring spending, with the amount committed to bills taken out of the budget, which is the variable share on its own, and the pace guide is measured against the part of the budget not committed to bills. Variable categories that trade off against each other, dining, coffee, and entertainment, can be marked Flex to draw from one shared flex budget. See Recurring bills in your budget, Tracking your spending pace, and Flex spending for the details, or get started with Zypper to see your own committed share.