Money words, de-fanged
A useful budget starts with a few ordinary concepts: what came in, what must go out, what can wait, and what protects you from surprise. These 12 plain-English definitions cover the terms most budgeting apps use, with examples showing what each one changes in a real monthly plan.
Annual percentage rate (APR)
The yearly price of borrowing, expressed as a percentage and including interest plus certain fees. A credit card with a 24% APR does not simply add 24% once; interest is usually calculated daily. Compare APRs when choosing between similar loans, but also compare total fees and payoff time.
Cash flow
The timing and amount of money entering and leaving your accounts. You can earn enough for the month and still have a cash-flow problem if rent leaves on the first and payday lands on the fifth. A calendar view or paycheck budget helps expose that gap.
Compound interest
Interest calculated on both the original amount and earlier interest. It helps savings grow and makes revolving debt expensive. At a 5% annual yield, $1,000 earns interest; later, the new interest earns interest too. Time matters as much as the advertised rate.
Discretionary expense
A cost you can reduce or pause without immediately losing a necessity: restaurant meals, entertainment and optional subscriptions are common examples. “Discretionary” does not mean shameful. It means adjustable when your plan needs room.
Emergency fund
Cash reserved for unplanned, necessary expenses such as urgent travel, a medical deductible or car repair. A small first target of $500 to $1,000 can prevent a surprise from becoming high-interest debt; a later target may cover several months of essential expenses.
Fixed expense
A bill that is usually the same amount on a predictable schedule, such as rent or a fixed-rate loan payment. Fixed does not mean permanent: you may be able to refinance, move or cancel later, but the number is stable in this month’s plan.
Net income
The money that reaches you after taxes, payroll deductions and other withholding. Build a spending plan from net income, not the larger gross figure printed before deductions. For irregular work, use the amount actually paid during the budgeting period.
Net worth
What you own minus what you owe. Add cash, investments and reasonable asset values; subtract credit cards, loans and other debts. It is a long-term direction marker, not a character grade, and it can improve while a monthly budget feels tight.
Rolling balance
Unspent category money carried into the next budgeting period. If you budget $80 for repairs and spend $20, a rolling category begins next month with $60. This is useful for costs that are predictable over a year but uneven month to month.
Sinking fund
Money saved gradually for a known future cost. Divide a $600 annual insurance bill by 12 and set aside $50 monthly. Unlike an emergency fund, a sinking fund prepares for something expected: holidays, tires, tuition or an annual subscription.
Variable expense
A necessary or optional cost whose amount changes, such as groceries, electricity or fuel. Estimate it from several recent months, then adjust for seasonality. Treating every variable expense as discretionary can produce a budget that looks strict but fails in real life.
Zero-based budget
A plan that gives every dollar of expected income a job: spending, saving, debt repayment or giving. Income minus planned allocations equals zero; your bank balance does not. The method is central to EveryDollar and YNAB, although their workflows differ.
Ready to turn the definitions into a system? Use our budgeting-app selection guide or compare the seven best apps we tested in 2026.