How our calculators work

General principles

• Everything runs in your browser. No inputs are transmitted or stored.
• Monthly compounding. Growth calculations convert your annual rate to a monthly rate (annual rate ÷ 12) and compound monthly, with monthly contributions added at the end of each month.
• Nominal dollars. Unless a calculator says otherwise, results aren't adjusted for inflation. To think in today's dollars, subtract expected inflation from your return assumption. Our inflation guide explains why.
• Sources are cited on the page wherever outside data is used.

Compound Interest Calculator

Future value = P × (1 + r)ⁿ + C × [(1 + r)ⁿ − 1] ÷ r, where P is your starting amount, C your monthly contribution, r the monthly rate (annual ÷ 12), and n the number of months. The rate comparison chart runs the same formula at 0%, 1% through 10%, 12%, 15%, 20% and 25%.

Limitations: this assumes a constant return every month. Real returns vary, and the order of returns matters when you're adding or withdrawing money. See sequence-of-returns risk. Fees and taxes aren't deducted. See how fees compound.

Retirement Number Calculator

1. Monthly shortfall = (essential + discretionary monthly expenses) − (Social Security + pension income).
2. Assets needed = annual shortfall ÷ your chosen "income rate", the percentage of your portfolio you expect to draw as income each year. At 5%, each $1 of annual shortfall requires $20 of assets. At 4%, it requires $25.
3. Required growth rate: the calculator solves, by numerical search, for the annual return that grows your current savings plus monthly contributions to the assets-needed figure by your retirement age, using the compounding formula above.

Limitations: expenses are in today's dollars while growth is nominal, so the result understates the target if inflation is significant. The income rate is your assumption. Research such as Morningstar's puts a conservative starting withdrawal rate near 4% for a 30-year retirement. See our guide to how much you need to retire. Taxes on withdrawals aren't modeled.

Net Worth Calculator

Net worth = total assets (cash, investments, retirement accounts, real estate, vehicles, business equity, other) − total liabilities (mortgage, auto loans, student loans, credit cards, other debt).

Comparison data: median household net worth by age of head of household from the Federal Reserve's 2022 Survey of Consumer Finances, the most recent complete survey: under 35, $39,000; 35–44, $135,600; 45–54, $247,200; 55–64, $364,500; 65–74, $409,900; 75 and over, $335,600. Medians are in 2022 dollars and describe households, not individuals.

Buy, Borrow, Die Calculator

• Borrowing capacity = (stocks + real estate) × your maximum loan-to-value percentage.
• Tax if you sold instead: annual draw × your capital gains tax rate. This is a simplification. It treats the entire amount sold as taxable gain, which overstates the tax when your cost basis is significant. It's most accurate for highly appreciated assets.
• Projection: each year, assets grow at your growth rate, and the loan balance grows at your interest rate plus that year's draw (interest compounds annually and isn't paid down). Years where the loan-to-value ratio exceeds your limit are flagged.
• At death: "gain erased" = final asset value − your cost basis, reflecting the step-up in basis heirs generally receive under federal tax law. "Net to heirs" = final asset value − loan balance, before any estate tax, state taxes or costs.

Limitations: real securities-backed loans have variable rates, lender-set advance rates by asset type, and maintenance calls that can force sales when markets fall. The calculator's smooth growth doesn't model a market drop. Read the risks and how step-up in basis works before relying on these results.

Debt Payoff Calculator

Each month: interest = balance × (APR ÷ 12). Then new balance = balance + interest − payment. This repeats until the balance reaches zero, capped at 100 years. The calculation runs twice, once at your payment and once with your extra payment added. If the payment doesn't exceed the first month's interest, the calculator reports that the debt will never be paid off.

Limitations: it assumes a fixed rate, a fixed payment and no new charges. Real credit cards may compound daily, and minimum payments usually shrink as the balance falls.

Social Security Claiming Age Calculator

Full retirement age comes from your birth year using SSA's schedule. For each claiming age, the benefit equals your full-retirement-age benefit × an adjustment factor. Before FRA, the factor is reduced by 5/9 of 1% per month for up to 36 months, then 5/12 of 1% per month beyond that. After FRA, it's increased by 2/3 of 1% per month (8% per year) up to age 70. Lifetime totals = monthly benefit × 12 × (planning age − claiming age). The break-even age between two claiming ages A1 < A2 with benefits B1 < B2 is (B2 × A2 − B1 × A1) ÷ (B2 − B1).

Limitations: claiming ages are whole years; results are in today's dollars with no cost-of-living adjustments, taxes, discounting, earnings test, or spousal and survivor benefits.

Roth vs. Traditional Calculator

Both scenarios start from the same annual pre-tax dollars (C). Traditional: C is invested each year, grown at your return for your years to retirement (future value of an annual annuity, contributions at year end), then multiplied by (1 − retirement tax rate). Roth: C × (1 − current tax rate) is invested each year and grown the same way, with no tax at withdrawal.

Limitations: it uses a single flat rate at each stage, ignores contribution limits, RMDs, state tax changes, employer matches and income phase-outs, and assumes qualified Roth withdrawals.

Inflation Calculator

Past to present: equivalent value = amount × CPI(to year) ÷ CPI(from year), using CPI-U annual averages (1982–84 = 100) from 1913 through 2025, published by the Bureau of Labor Statistics and compiled by the Federal Reserve Bank of Minneapolis. Average annual inflation = (CPI ratio)^(1 ÷ years) − 1. Future: future cost = amount × (1 + rate)^years, and future purchasing power = amount ÷ (1 + rate)^years.

Limitations: annual averages smooth out month-to-month changes, and the CPI reflects an average urban consumer's basket, which may differ from yours.

Personal Inflation Rate Calculator

Your rate = Σ (monthly spend in each category × that category's 12-month CPI change) ÷ total monthly spend. Extra annual cost = Σ (monthly spend × 12 × category change). Category changes come from the BLS CPI release for August 2026: rent of primary residence (+2.7%), owners' equivalent rent (+3.1%), food at home (+2.2%), food away from home (+3.4%), gasoline (+27.4%), electricity (+3.8%), new vehicles (+0.6%), motor vehicle insurance (−5.1%), medical care services (+2.5%), apparel (+3.6%), and core CPI, all items less food and energy (+2.4%), for everything else. A fixed-rate mortgage payment is treated as 0%.

Limitations: national averages, so local prices may differ; it assumes you buy the same things in the same amounts; and it shows the last 12 months, not a forecast.

Review and corrections

We review each calculator and its data sources periodically and whenever tax law or source data changes. If you believe something is wrong, please contact us.