How we calculate: Finance

EMI = P × r × (1+r)ⁿ ÷ [(1+r)ⁿ − 1] P = principal, r = monthly interest rate, n = number of monthly payments The standard fixed-rate amortizing-loan formula, derived from the present-value-of-an-annuity equation used across fixed-income lending — the same math the CFPB describes for how a mortgage or installment loan pays down.

• Consumer Financial Protection Bureau — How does paying down a mortgage work? — accessed 2026-08-20

Loan amount = Home price − Down payment Monthly payment uses the standard amortization formula applied to that loan amount Same present-value-of-an-annuity formula used for any fixed-rate amortizing loan — see the CFPB's consumer explainer on how mortgage paydown works.

• Consumer Financial Protection Bureau — How does paying down a mortgage work? — accessed 2026-08-20

A = P(1 + r/n)^(nt) plus the future value of any monthly contribution series added on top The standard compound-interest formula, as explained in the U.S. SEC's Investor.gov educational materials — A is the future balance, P the principal, r the annual rate, n the compounding frequency per year, and t the number of years.

• Investor.gov (U.S. SEC) — What is compound interest? — accessed 2026-08-20

Uses the same EMI formula as the Loan EMI calculator, then tracks the running balance month by month to show how the principal/interest split shifts across the loan's life. Same present-value-of-an-annuity amortization math described in the CFPB's guide to how mortgage/loan paydown works, applied month by month rather than as a single payment figure.

• Consumer Financial Protection Bureau — How does paying down a mortgage work? — accessed 2026-08-20

Future value = current savings compounded to retirement age, plus the future value of monthly contributions Estimated monthly income = (Projected balance × 4%) ÷ 12 The 4% figure traces to William Bengen's 1994 study "Determining Withdrawal Rates Using Historical Data" (Journal of Financial Planning), which found a 4% first-year withdrawal, adjusted for inflation thereafter, held up across historical 30-year U.S. market periods for a 50-75% stock portfolio. It's a widely cited planning heuristic, not a guarantee for any individual's actual portfolio or timeframe.

• Bengen WP — Determining Withdrawal Rates Using Historical Data (Journal of Financial Planning, Oct 1994) — accessed 2026-08-23

Tax = Σ (income within each bracket × that bracket's rate), applied progressively from the lowest bracket upward

Bracket rates are published tax-year figures for the stated jurisdiction and year (India FY 2026-27 New Regime; USA 2026 single-filer federal brackets), but this tool applies them to gross income only — it does not subtract the standard deduction, India's Section 87A rebate, other credits, or add surcharge/cess. Your actual liability will differ. Always confirm with your local tax authority.

• IRS — Tax inflation adjustments for tax year 2026 (Rev. Proc. 2025-32) — accessed 2026-08-20
• Income Tax Department (India) — New vs Old Tax Regime FAQs — accessed 2026-08-20

Net cost of buying = all cash paid (down payment + monthly principal & interest + tax + insurance + maintenance) − net sale proceeds (home value − remaining loan balance − selling costs) at the chosen horizon Net cost of renting = total rent paid − the future value of the down payment if it had been invested instead Whichever net cost is lower is the cheaper option over that horizon. This opportunity-cost framing — crediting the buyer with home equity but crediting the renter with investment growth on the money they didn't tie up — is the same approach the CFPB points to when it notes that many mortgage calculators only account for principal and interest, missing tax, insurance, maintenance, and what the down payment could otherwise have earned.

• Consumer Financial Protection Bureau — Making the decision to rent or buy — accessed 2026-08-25

Front-end limit = 28% × gross monthly income (covers principal, interest, tax, and insurance — PITI) Back-end limit = 36% × gross monthly income − other monthly debts Maximum monthly housing budget = the smaller of the two The maximum home price is then solved so that its principal & interest payment plus its estimated tax and insurance exactly fill that monthly budget, given your down payment, rate, and term. Widely known as the 28/36 rule — a guideline, not a law, that most conventional mortgage underwriting still references.

• Bankrate — What is the 28/36 rule? — accessed 2026-08-25

Employee contribution = salary × contribution %, capped at the IRS annual limit Employer match = salary × min(contribution %, match cap %) × match rate Balance grows each year as: balance × (1 + return) + (employee + employer contributions) The 2026 IRS employee elective-deferral limit is $24,500 (there are additional catch-up limits for ages 50+ and 60-63 under SECURE 2.0, not modeled as separate inputs here — see the FAQ).

• IRS — 401(k) limit increases to $24,500 for 2026 — accessed 2026-08-25

Break-even point (months) = total closing costs ÷ monthly savings Monthly savings = current monthly payment − new monthly payment Both monthly payments use the standard fixed-rate amortizing-loan formula. If refinancing doesn't actually lower your payment, there's no break-even point to calculate — the calculator reports that plainly rather than showing a nonsensical negative number.

• Chase — Calculating the break-even point when refinancing — accessed 2026-08-25

Every debt's minimum payment is made each month; any extra budget is routed entirely to one priority debt at a time — the highest-APR debt under the avalanche method, or the smallest-balance debt under the snowball method — until that debt is paid off, at which point its former payment amount (minimum plus any leftover extra) rolls onto the next priority debt. This is the standard mechanic behind both named strategies, as described by the CFPB's own debt-reduction guidance.

• Consumer Financial Protection Bureau — How to reduce your debt — accessed 2026-08-25

Needs target = income × 50% Wants target = income × 30% Savings target = income × 20% The 50/30/20 rule, popularized by Elizabeth Warren and Amelia Warren Tyagi in their 2005 book 'All Your Worth: The Ultimate Lifetime Money Plan' — a rule of thumb, not a formula tied to any single household's actual costs.

• The Balance — The 50/30/20 Budget Rule of Thumb — accessed 2026-08-25

Future value of contributions = X × [((1+r)ⁿ − 1) ÷ r] × (1+r) — the standard future-value-of-an-annuity-due formula, treating each year's contribution as invested at the start of that year Roth after-tax value = future value (withdrawals are tax-free) Traditional after-tax value = future value × (1 − retirement tax rate) This compares the same nominal annual contribution amount in both accounts — it does not model investing the extra tax refund a Traditional contribution generates today, which is a real but smaller secondary effect some more detailed comparisons include.

The 2026 IRA contribution limit is $7,500 combined across all Traditional and Roth IRAs you own ($8,600 if you're 50 or older) — this calculator caps the modeled contribution at $7,500 and flags it if your entry exceeds that.

• Vanguard — Roth IRA income and contribution limits for 2026 — accessed 2026-08-25

Target = essential monthly expenses × number of months of coverage The CFPB deliberately doesn't prescribe one fixed number of months — its own guidance frames the right target as depending on your situation and the kinds of unexpected expenses you're most likely to face. The 3-6-9 month range offered here reflects the commonly cited industry rule of thumb, not an official CFPB figure.

• Consumer Financial Protection Bureau — An essential guide to building an emergency fund — accessed 2026-08-25

Gain = sale price − cost basis Long-term gains use the 2026 single-filer capital-gains brackets — 0% up to $49,450 of total income, 15% from $49,450 to $545,500, 20% above — applied only to the portion of the gain that falls in each bracket after your other income fills the brackets below it. Short-term gains (held ≤1 year) are taxed as ordinary income, using the same 2026 single-filer federal brackets as this site's Income Tax Calculator, stacked the same way on top of your other income.

Single-filer federal figures only — married-filing-jointly thresholds are higher, and state capital gains taxes (where they apply) aren't included. High earners may also owe the 3.8% Net Investment Income Tax on top of this estimate; see the FAQ.

• Kiplinger — IRS updates capital gains tax thresholds for 2026 — accessed 2026-08-25

Taxable earnings = net profit × 92.35% Social Security portion = min(taxable earnings, $184,500) × 12.4% Medicare portion = taxable earnings × 2.9% Additional Medicare Tax = max(0, taxable earnings − $200,000) × 0.9% (single filer) The 92.35% factor and the split rates come directly from IRS Schedule SE — it exists because a traditional employee's employer pays half of FICA tax on their behalf (7.65%), income a self-employed person never has withheld in the first place, so the 15.3% combined rate applies to a slightly reduced base instead.

Only federal self-employment tax is estimated here — this is in addition to, not instead of, federal and state income tax on the same profit. Only the 'regular' 15.3% (Social Security + Medicare) portion gets the above-the-line half-deduction; the 0.9% Additional Medicare Tax is never deductible.

• Payroll.org — Social Security wage base increases to $184,500 for 2026 — accessed 2026-08-25

Coverage need = Debt + (Annual income × years of replacement) + Mortgage balance + Education costs − existing savings & coverage The DIME method (Debt, Income, Mortgage, Education), a named approach used across the life insurance industry as a more specific alternative to flat income-multiple rules of thumb, since it accounts for your actual obligations rather than a single generic multiplier.

• NerdWallet — How much life insurance do I need? — accessed 2026-08-25

Annual property tax = assessed value × local effective tax rate Property tax rates are set entirely locally (by county, city, and school district), not federally — this is simple arithmetic on the rate you supply, not a lookup of your specific jurisdiction's actual rate.

"Assessed value" is often not the same as market value — many jurisdictions apply an assessment ratio, cap annual increases (like California's Proposition 13), or reassess only periodically. Check your county assessor's site for your property's actual current assessed value rather than assuming it equals what you'd sell the home for.

• Tax Foundation — property tax rates by state — accessed 2026-08-25

Available equity = (home value × max CLTV%) − existing mortgage balance Monthly payment uses the standard amortizing-loan formula (the same one behind this site's own Mortgage Calculator) applied to the available-equity amount, rate, and term you enter — modeling it as a fixed-term home equity loan rather than a revolving HELOC line, since a line of credit's payment depends on how much of it you actually draw and when.

Most lenders cap combined loan-to-value (existing mortgage + new borrowing, divided by home value) at 80-85%, though this varies by lender and credit profile. A HELOC itself is usually a variable-rate revolving line, not a fixed-payment loan — this calculator's payment estimate assumes you borrow and repay the full available amount as a fixed-rate home equity loan instead, which is the more predictable of the two products to model.

• Experian — How much can you borrow with a HELOC? — accessed 2026-08-25

Closing costs ≈ loan amount × 2% to 5% Covers lender fees (origination, application, underwriting), third-party fees (appraisal, title search and insurance, credit report), recording fees, and prepaid items (homeowners insurance, property tax escrow) — the commonly cited range across mortgage-industry sources for a home purchase. Actual costs vary by lender, loan type, location, and negotiated seller credits.

This estimates a purchase mortgage's closing costs. A refinance typically runs somewhat lower as a share of the loan (no new title insurance policy is always required, for instance) — see this site's Mortgage Refinance Calculator, which cites a separate 3-6% refinance-specific range from Chase.

• LendingTree — How much are closing costs? Average costs and fees — accessed 2026-08-25

Maximum monthly transportation budget = gross monthly income × 10% Maximum loan payment = that budget − your other monthly car costs Maximum loan amount = present value of that payment over a 4-year (48-month) term at your interest rate Maximum vehicle price = maximum loan amount + your down payment The 20/4/10 rule — 20% down, a loan term of 4 years or less, transportation costs at or under 10% of gross income — a widely cited car-affordability guideline covered by Chase, J.D. Power, and other major auto and financial publishers.

The 48-month loan term is fixed to match the rule itself, not user-adjustable — a longer term would let you "afford" a more expensive car on paper while paying more total interest, defeating the rule's purpose.

• Chase — The 20/4/10 rule for buying a car — accessed 2026-08-25

Balance grows monthly as: balance × (1 + monthly return) + monthly contribution, compounded across the number of months until enrollment. 529 plans grow federally tax-free, and withdrawals are also federal-tax-free when used for qualified education expenses (tuition, fees, room and board, and more) — the core reason a 529 is generally favored over a taxable account for this specific goal, per IRS and SEC investor-education guidance.

Contributions to a 529 count as gifts for tax purposes. A single contributor can give up to the annual gift tax exclusion ($19,000 for 2026) per beneficiary without filing a gift tax return, and 529 plans specifically allow "superfunding" — electing to treat a lump sum of up to 5 years' worth of that exclusion ($95,000 single, $190,000 married for 2026) as spread evenly over 5 years for gift-tax purposes. This calculator doesn't model lump-sum superfunding directly — enter an equivalent average monthly contribution instead.

• SEC Office of Investor Education — An Introduction to 529 Plans — accessed 2026-08-25