Money Calculator Formulas 2026 — the open dataset behind every tool
These are the exact formulas and default inputs behind all 30 MoneyCalcs calculators. Each calculator runs the formula shown here in your browser — nothing is hidden and nothing is hardcoded per page. License: CC BY 4.0 — reuse anywhere with attribution to MoneyCalcs formula data.
Machine-readable copies: llms.txt · llms-full.txt · ai/summary.json · ai/faq.json
| Calculator | Category | Formula / method | Default inputs |
|---|---|---|---|
| Mortgage Calculator | Loans & Mortgage | The monthly principal & interest payment uses the standard amortization formula: M = P·r / (1 − (1+r)^−n), where P is the loan amount, r the monthly rate (APR ÷ 12) and n the number of months. Property tax and insurance are added as flat monthly costs, which is how escrow works at most US lenders. | Home price ($) = 400,000, Down payment ($) = 80,000, Interest rate (% APR) = 6.5, Loan term (years) = 30, Property tax (% of price / year) = 1.2, Home insurance ($/year) = 1,200 |
| How Much House Can I Afford | Loans & Mortgage | Affordable housing budget = monthly gross income × 0.36 − other monthly debts − monthly property tax − monthly insurance. That budget is converted to a maximum loan amount with the same amortization formula as the mortgage calculator, then your down payment is added back. | Gross annual income ($) = 90,000, Other monthly debt payments ($) = 400, Down payment ($) = 40,000, Mortgage rate (%) = 6.5, Term (years) = 30, Property tax ($/year) = 4,800, Insurance ($/year) = 1,200 |
| Car Loan Calculator | Loans & Mortgage | Amount financed = price − down − trade-in (+ sales tax where applicable). Monthly payment = amortized payment on that amount. Total cost = price + all interest paid over the term. | Car price ($) = 35,000, Down payment ($) = 3,000, Trade-in value ($) = 0, APR (%) = 7.5, Term (years) = 5, Sales tax (%) = 6 |
| Loan Calculator | Loans & Mortgage | M = P·r / (1 − (1+r)^−n). Total interest = M·n − P. This is the same formula banks use for any fixed-rate installment loan. | Loan amount ($) = 20,000, APR (%) = 9, Term (years) = 5 |
| Credit Card Payoff Calculator | Debt Payoff | Each month: interest = balance × APR/12, then your payment covers interest first and the rest reduces principal. If your payment is below the monthly interest, the balance grows and never clears — the calculator warns you. | Card balance ($) = 5,000, APR (%) = 22, Monthly payment ($) = 200, Extra payment ($/mo, optional) = 0 |
| Student Loan Payoff Calculator | Debt Payoff | Same month-by-month amortization as credit cards: interest accrues on the remaining balance, extra payments go entirely to principal and compound your savings. | Loan balance ($) = 30,000, Interest rate (%) = 6.5, Monthly payment ($) = 342, Extra payment ($/mo, optional) = 0 |
| Debt Snowball Payoff Calculator | Debt Payoff | Each line should be: balance, APR (example: 3200 14.5). The calculator accrues monthly interest on every balance, pays the smallest first with your full budget, and simulates month by month until everything hits zero. | Debts (balance APR — one per line) = 5200 21.9 3200 14.5 11500 6.5, Total monthly payment budget ($) = 1,000 |
| Compound Interest Calculator | Savings & Investing | Future value = lump sum × (1+i)^months + monthly contribution × ((1+i)^months − 1)/i, where i = rate/12. Contributions are assumed at month-end (ordinary annuity). | Initial investment ($) = 10,000, Monthly contribution ($) = 500, Annual return (%) = 7, Years = 30 |
| Retirement Calculator | Savings & Investing | Projection: current savings grow at the pre-retirement return, plus monthly contributions compounded. Needed: desired annual income × 25, so that withdrawing 4%/yr historically doesn't deplete the portfolio over 30 years. | Current age = 30, Retirement age = 65, Current savings ($) = 50,000, Monthly contribution ($) = 750, Expected annual return (%) = 7, Desired annual retirement income ($) = 60,000 |
| Savings Goal Calculator | Savings & Investing | Required monthly = (goal − future value of current savings) × i / ((1+i)^n − 1), where i is the monthly rate and n the months to your deadline. Set rate to 0 for a cash goal under a mattress. | Goal amount ($) = 30,000, Already saved ($) = 2,000, Years to deadline = 3, Annual interest (%) = 4 |
| Emergency Fund Calculator | Savings & Investing | Target = essential monthly expenses × months of coverage. Gap = target − current savings. Monthly plan = gap ÷ months you give yourself. | Essential monthly expenses ($) = 3,500, Months of coverage = 6, Already saved ($) = 1,000, Reach goal in (months) = 18 |
| FIRE Calculator | Savings & Investing | FI number = annual spending ÷ withdrawal rate (4% default → spending × 25). The calculator then simulates monthly portfolio growth with your contributions until it crosses the target. | Annual spending ($) = 40,000, Current investments ($) = 100,000, Saving per year ($) = 30,000, Expected return (%) = 7, Safe withdrawal rate (%) = 4, Current age = 30 |
| Salary / Take-Home Pay Calculator | Salary & Income | Taxable income = gross − standard deduction ($16,100 single / $32,200 joint in 2026). Federal tax accrues bracket by bracket. FICA = 6.2% Social Security (capped at $184,500) + 1.45% Medicare + 0.9% surtax above $200k/$250k. State tax is entered as a flat % — check your state's rate (0% in TX, FL, NV, WA…; up to ~10% in CA). | Gross pay = 80,000, Pay period = yearly, Hours/week (if hourly) = 40, Filing status = single, State income tax (% — flat estimate) = 5 |
| Hourly to Salary Calculator | Salary & Income | Annual = hourly × hours per week × 52. Bi-weekly and weekly figures divide accordingly. All values are pre-tax; run the salary calculator for take-home. | Hourly rate ($) = 28, Hours per week = 40 |
| Salary to Hourly Calculator | Salary & Income | Hourly = annual ÷ 52 weeks ÷ hours per week. All pre-tax. | Annual salary ($) = 75,000, Hours per week = 40 |
| Freelance Rate Calculator | Salary & Income | Required gross = (target income + annual expenses) ÷ (1 − tax rate). Billable hours = hours per week × billable weeks per year (nobody bills 52). Rate = gross ÷ billable hours. | Target take-home per year ($) = 60,000, Business + benefits costs ($/mo) = 500, Tax rate (%) = 28, Billable hours per week = 30, Billable weeks per year = 44 |
| Side Hustle Income Calculator | Salary & Income | Gross = rate × weekly hours × weeks. Net = gross − tax − annual costs. Effective hourly = net ÷ hours actually worked, which is the number to compare against your day job. | Hourly rate or earnings ($) = 35, Hours per week = 8, Weeks per year = 48, Tax rate (%) = 25, Costs ($/month) = 50 |
| Paycheck Calculator | Salary & Income | Federal tax uses 2026 brackets and the standard deduction for your filing status; FICA is 6.2% SS (wage base $184,500) + 1.45% Medicare (+0.9% above $200k/$250k). State tax is your flat % input. | Gross pay = 3,500, Pay period = monthly, Hours/week (if hourly) = 40, Filing status = single, State income tax (%) = 5 |
| 50/30/20 Budget Calculator | Life & Spending | Each category is a fixed share of take-home income. If needs exceed 50%, the overflow comes out of wants first — protect the 20% savings floor. | Monthly take-home pay ($) = 4,500 |
| Inflation Calculator | Life & Spending | Future equivalent = amount × (1 + rate)^years. Today's-equivalent divides instead. US long-run CPI inflation is ~3%; recent years ran hotter. | Amount ($) = 10,000, Annual inflation (%) = 3, Years = 10 |
| Net Worth Calculator | Life & Spending | Net worth = (cash + investments + home + car + other) − (mortgage + loans + cards + other debts). It can be negative early in a career — what matters is the trend. | Cash & savings ($) = 15,000, Investments/retirement ($) = 40,000, Home market value ($) = 0, Car value ($) = 8,000, Other assets ($) = 0, Mortgage balance ($) = 0, Student/other loans ($) = 12,000, Credit card debt ($) = 2,000, Other debts ($) = 0 |
| Rent Affordability Calculator | Life & Spending | Max rent = monthly gross income × 30%. Income needed = target rent ÷ 0.30 × 12. A 25% version is shown as the safer budget for anyone carrying debt or building savings. | Gross annual income ($) = 60,000, Rent you're eyeing ($/mo) = 1,600 |
| Cost of Living / Moving Salary Calculator | Life & Spending | Ratio = target city basket ÷ current city basket. Required salary = current salary × ratio. Basket comparison tracks moving sites' methodology closely enough for a decision. | Current salary ($) = 90,000, Current city basket ($/mo) = 2,800, Target city basket ($/mo) = 3,600 |
| Tip Calculator with Split | Life & Spending | Tip = bill × tip%. Total = bill + tip. Per person = total ÷ people. Tip on the pre-tax amount is standard practice; on post-tax is generous. | Bill amount ($) = 85, Tip (%) = 18, Split between (people) = 2 |
| Vacation Budget Calculator | Life & Spending | Total = travel + lodging×days + food×days + activities + misc. Per person divides by party size; the savings row spreads it over 12 months. | Flights/transport total ($) = 800, Lodging ($/night) = 150, Days = 7, Food ($/person/day) = 60, Activities total ($) = 300, Misc/buffer ($) = 200, Travelers = 2 |
| Wedding Budget Calculator | Life & Spending | Total = sum of all categories. Per-guest = total ÷ guest count (catering and favors scale with heads; venue and photo don't). Savings row spreads the total over your planning window. | Venue ($) = 6,000, Catering & bar ($) = 9,000, Photo & video ($) = 3,500, Attire & beauty ($) = 2,500, Flowers & decor ($) = 2,000, Music/DJ ($) = 1,500, Other ($) = 2,500, Guests = 80, Months until wedding = 18 |
| Baby Cost Calculator | Life & Spending | Total = monthly × 12 × years + one-time costs. The per-month row amortizes one-time costs across the period. | Ongoing monthly cost ($) = 900, Years to model = 5, One-time costs ($) = 3,500 |
| Quit Smoking Savings Calculator | Life & Spending | Daily cost = cigarettes/day ÷ pack size × pack price. Yearly × 365. If invested, the annual savings are modeled as monthly contributions compounding at your chosen return. | Cigarettes per day = 12, Pack size = 20, Pack price ($) = 9, Years smoke-free = 20, Invest savings at (%) = 7 |
| State Income Tax Calculator | Salary & Income | Taxable income = gross − standard deduction (2026: $16,100 single / $32,200 joint / $24,150 HoH) − pre-tax deductions. Federal tax applies the 2026 IRS brackets (10–37%). FICA = 6.2% Social Security up to the $184,500 wage base + 1.45% Medicare + 0.9% additional Medicare above $200k. State tax comes from the live 2026 state database — nine states (TX, FL, WA, NV, SD, WY, TN, AK, NH) charge no income tax on wages. | Gross annual income ($) = 85,000, State = CA, Filing status = single, Pre-tax deductions ($/year, e.g. 401k) = 0 |
| IBAN Validator & Checker | Life & Spending | IBAN = country code + 2 check digits + BBAN (bank/account number, up to 30 alphanumeric chars). Validation: move the first 4 chars to the end, convert letters to numbers (A=10 … Z=35), compute mod 97 — a valid IBAN leaves remainder 1 (ISO 7064/13616). The checksum catches typos but not fake accounts, so the bank lookup confirms the number is actually registered. | IBAN = DE89370400440532013000 |
Standard 2026 US rules and rates where applicable (federal tax brackets, FICA cap, amortization). Formulas are planning estimates, not financial or tax advice — verify against official sources before big decisions.