Monthly Budget Planner
Calculate your monthly cash surplus or deficit by subtracting fixed and variable expenses from your monthly take-home income. Use it as the simplest budgeting check to see whether you live within your means and how much is left for savings, debt payoff, or discretionary spending each month.
Last updated: May 2026
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About this calculator
The formula is: monthly surplus = monthly income − fixed expenses − variable expenses. A positive result means you have money left to save, invest, or pay down debt; a negative result means you spend more than you earn and need to either cut expenses or raise income to avoid accumulating debt. Fixed expenses are obligations that stay roughly the same every month: rent or mortgage, insurance premiums, loan payments, subscriptions, daycare, gym memberships. Variable expenses fluctuate with behavior: groceries, gas, restaurants, entertainment, clothing, household supplies. Use net (after-tax) income, since that's what actually hits your account; the gross figure overstates available money by 20–35% depending on tax bracket and 401(k) contributions. Edge cases: if either expense category equals or exceeds income, surplus is zero or negative — a clear signal to act. Annual or irregular costs (insurance premiums paid yearly, car registration, holiday gifts, vacations) should be converted to monthly equivalents by dividing the annual amount by 12 and including them in fixed expenses; ignoring them produces an overoptimistic surplus that gets wiped out when the annual bill arrives. A useful benchmark: aiming for a 20%+ surplus relative to take-home income gives meaningful room to save aggressively, pay down debt, and absorb unexpected costs without panic.
How to use
Example 1 — Stable single income. Take-home income $5,200/month. Fixed expenses: rent $1,400, car loan $360, insurance $180, phone/internet $120, gym $40, streaming $35 = $2,135. Variable: groceries $550, gas $180, restaurants $220, entertainment $100, household supplies $80 = $1,130. Enter 5200, 2135, and 1130. Result: $1,935 surplus. Verify: 5200 − 2135 − 1130 = 1,935. ✓ A 37% surplus is excellent — plenty of room to fully fund retirement, build an emergency fund, and still enjoy life. Example 2 — Tight budget with annual costs amortized. Take-home $4,000/month. Fixed: rent $1,500, car loan $320, insurance $145, phone $80, daycare $700, annual costs amortized (car registration + holiday gifts + vacation) $230/month = $2,975. Variable: groceries $480, gas $150, restaurants $90, household $90 = $810. Enter 4000, 2975, and 810. Result: $215 surplus. Verify: 4000 − 2975 − 810 = 215. ✓ A 5% surplus is tight — emergencies will quickly turn this into a deficit, so the priority is either reducing fixed expenses (especially the largest line items: rent and daycare) or increasing income before adding new commitments.
Frequently asked questions
Should I use gross or net (after-tax) income in this calculator?
Use net (take-home) income, which is what actually arrives in your bank account each pay period after federal income tax, state income tax, Social Security, Medicare, health insurance premiums, and 401(k) contributions are subtracted. Gross income overstates available money by 20–35% depending on bracket, state, and pre-tax deductions, and budgeting against gross will leave you short every month. If you have variable income (commission, freelance, bonuses), use a conservative average of the last 6–12 months of net deposits, not the high-water mark. For irregular pay frequencies (biweekly, weekly), convert to monthly equivalent: biweekly × 26 ÷ 12 = monthly, weekly × 52 ÷ 12 = monthly. Always use post-tax dollars because all your expenses are paid in post-tax dollars.
How do I handle annual or irregular expenses?
Convert them to monthly equivalents and include them in fixed expenses. Add up everything that's not monthly (car insurance paid every 6 months, registration, annual subscriptions, property taxes if not in escrow, holiday gifts, vacations, summer camp, Christmas, birthdays) and divide by 12 to get a monthly figure. A useful method: open a separate "annual buffer" savings account, transfer this monthly equivalent into it automatically, then pay the lumpy expenses from that account when they arrive. This smooths out cash flow and prevents the common pattern of constant minor budget shocks that drain emergency savings. Most households underestimate annual costs by 30–50% when first making a budget — running a 12-month review of past bank and credit-card statements is the only reliable way to capture them all.
What is a healthy monthly surplus?
A useful target is 15–25% of take-home income, allocated across emergency fund, retirement, and other savings goals. The 50/30/20 rule is a popular framework: 50% on needs (housing, food, transportation, insurance, minimum debt payments), 30% on wants (restaurants, entertainment, hobbies, travel), 20% on savings and extra debt payoff. Tighter budgets may run 60/30/10 or 70/20/10 with savings squeezed; aggressive savers target 50/20/30 or even 40/10/50 (the FIRE movement aims for 50%+ savings rates). The right ratio depends on income level, life stage, and goals. The most common pattern in financial trouble is 80–95% spent on needs and wants with only 5% or less for savings — a tiny surplus means a single emergency creates debt that takes months or years to pay off.
What are the most common mistakes people make budgeting?
The biggest is forgetting annual costs — most people budget for monthly bills but forget car registration, holiday gifts, vacations, and once-a-year insurance premiums, then are repeatedly surprised when these "unexpected" expenses hit. The second is using gross income instead of net, overstating real available money by 25–35%. The third is treating savings as "what's left over" rather than a line item; expenses expand to fill available income, so pay yourself first by transferring savings the day pay arrives. The fourth is creating a perfect budget on paper and then failing to track actual spending against it — the budget that you check weekly is more useful than the elegant budget you set up once and forget. The fifth is ignoring small recurring subscriptions; the typical household has $50–$150/month in subscriptions they're not actively using. Finally, people often set up budgets after a financial scare, follow them rigidly for two months, then drift back to old habits — sustainable budgets are slightly loose with built-in fun money so they actually get followed.
When should I not use this calculator?
Skip it for cash-flow planning over horizons longer than a month — this is a single-month snapshot, and longer-term planning requires modeling income changes, debt payoff schedules, and savings growth over time. It is the wrong tool for businesses or freelancers with highly variable income; for those, build a separate model based on conservative averages and seasonal patterns rather than a single-month figure. Do not use it for net worth or wealth tracking — surplus is a flow metric, not a stock metric, and a positive surplus doesn't automatically mean you're building wealth (you could be paying down debt rather than saving). For couples or households with shared finances, run the calculator on combined household figures, not individual ones, since most expenses are shared. And for major life decisions (buying a house, changing jobs, having a child), this calculator is a starting point but you need a more complete cash-flow projection that includes the change's effect over 2–5 years.