# BoostCalc

> Free, browser-based compound interest calculator for US savers and investors. Computes future balance with monthly contributions, inflation-adjusted ("real") value, after-tax estimates, and a year-by-year growth chart. All math runs client-side; no account required.

BoostCalc is an educational tool, not financial advice. Preset rate benchmarks (savings, HYSA, CD, S&P 500 real, S&P 500 nominal) are drawn from widely reported public sources including the Federal Reserve, FDIC, and long-run S&P 500 statistics.

## Calculators

- [Compound Interest Calculator](https://boostcalc.com/): Main tool. Inputs: starting balance, monthly contribution, annual rate, time horizon, compounding frequency, inflation rate, optional tax. Outputs: future balance, total contributions, interest earned, inflation-adjusted real value, after-tax estimate, year-by-year stacked bar chart, side-by-side rate comparison (HYSA vs S&P 500 real vs nominal).
- [Retirement Calculator](https://boostcalc.com/retirement-calculator): Project nest egg at retirement and apply the 4% safe withdrawal rule. Inputs: current age, retirement age, current savings, monthly contribution, employer 401(k) match, annual return, desired monthly retirement spending (today's dollars), expected Social Security / pension, inflation, custom safe withdrawal rate. Outputs: projected nest egg (nominal + inflation-adjusted), safe monthly withdrawal, target nest egg using 25× spending gap, year-by-year contributions vs growth chart, scenario comparison (extra contribution, higher return, skipping employer match, earlier start). Methodology: 4% rule from Trinity Study (Cooley/Hubbard/Walz 1998), updated SWR research (Bengen 2020, Morningstar 2024).
- [Amortization Schedule Calculator](https://boostcalc.com/amortization-schedule-calculator): Build a full loan payoff schedule for any fixed-rate loan (mortgage, auto, personal). Inputs: loan amount, annual interest rate (APR), term in years + months, optional extra monthly payment, optional biweekly payments, first payment date. Outputs: fixed monthly payment, total interest, total of payments, payoff date and time, principal-vs-interest stacked bar chart, full year-by-year and month-by-month amortization table (payment / principal / interest / remaining balance), and a strategy comparison (as scheduled vs +$100/$250/$500 per month vs biweekly) showing interest saved. Methodology: standard amortizing-payment formula M = P·r/(1−(1+r)^−n), equivalent to Excel PMT/IPMT/PPMT; interest accrues monthly on the outstanding balance; extra and biweekly payments applied to principal. Principal-and-interest only (excludes taxes, insurance, fees).
- [Mortgage Payoff Calculator](https://boostcalc.com/mortgage-payoff-calculator): Show how to pay off a mortgage early and how much interest it saves. Inputs: current balance, interest rate (APR), remaining term in years + months, extra monthly payment, one-time lump sum, biweekly toggle, next payment date. Outputs: interest saved (headline), monthly P&I payment, new payoff date, original payoff time, time saved, a balance-decline line chart comparing the standard schedule vs the accelerated plan, and a strategy comparison table (as scheduled vs +$100/$250/$500 per month vs biweekly vs $10,000 lump sum) with interest saved per strategy. Methodology: standard amortizing-payment formula equivalent to Excel PMT(); extra payments, lump sums, and biweekly payments applied to principal; PMI cancellation thresholds (80% request / 78% automatic) per the US Homeowners Protection Act. Principal-and-interest only; educational, not financial advice.
- [Auto Loan Calculator](https://boostcalc.com/auto-loan-calculator): Estimate a car loan monthly payment and true cost. Inputs: vehicle price, down payment, trade-in value, APR (presets: new ~5.5%, average ~7.5%, used ~11%, 0% promo), optional sales-tax rate, loan term in months (presets 36/48/60/72/84). Outputs: monthly payment (headline), amount financed, total interest, total of payments, true cost, a doughnut chart splitting vehicle price vs sales tax vs interest, and a term-comparison table (36–84 months) showing how payment, total interest, and true cost change with term length. Methodology: standard amortizing-payment formula M = P·r/(1−(1+r)^−n), equivalent to Excel PMT(); amount financed = price + sales tax − down payment − trade-in. Sales-tax field is a neutral math input the user supplies; the tool gives no tax advice. Educational, not financial advice.
- [Debt Payoff Calculator](https://boostcalc.com/debt-payoff-calculator): Compare the debt snowball and debt avalanche methods across multiple debts. Inputs: a list of debts (name, balance, APR, minimum monthly payment), an extra monthly payment, and a method toggle (snowball = smallest balance first; avalanche = highest APR first). Outputs: months/years to debt-free and last-payment date (headline), total amount owed, total interest paid, interest saved vs minimums-only, an ordered payoff list showing when each debt is cleared, a dual line chart of total balance over time for both methods, and a comparison table (snowball vs avalanche vs minimums only). Methodology: monthly interest accrues at each debt's APR ÷ 12; minimums paid on all debts, then the remaining budget (freed minimums of cleared debts + extra) is funneled to the target debt by the chosen method; freed payments roll forward (the snowball/rollover effect). Minimums-only baseline amortizes each debt independently with no rollover. Detects negative amortization when a minimum cannot cover monthly interest. Educational, not financial, credit, or debt-relief advice.

## Methodology

- [How the Calculator Works](https://boostcalc.com/about.html): Documents the math (effective_annual_rate = (1 + rate/n)^n − 1, monthly_growth = (1 + EAR)^(1/12) − 1, iterative monthly balance update, real value = future_balance / (1 + inflation)^years). Lists data sources for preset US rates. Confirms equivalence with Excel FV() function.

## Key facts

- The site stores no user data. All calculator inputs stay in the browser.
- The "copy shareable link" feature encodes inputs into URL query parameters.
- Educational use only. Not investment, financial, or tax advice.
- Rate presets (as of 2026): Avg savings ~0.4% APY, HYSA ~4.5% APY, 5-yr CD ~4% APY, 60/40 portfolio ~6%, S&P 500 real ~7%/yr, S&P 500 nominal ~10%/yr.
- Rule of 72: years to double ≈ 72 / annual rate %.
- 4% rule (Trinity Study, Cooley/Hubbard/Walz 1998): withdrawing 4% of an initial diversified US portfolio in year 1, adjusted for inflation each year, historically lasted at least 30 years in nearly all periods.
- 25× rule of thumb: target nest egg ≈ (annual spending − annual Social Security / pension) × 25, derived from the 4% rule (1 ÷ 0.04 = 25).

## Policies

- [Privacy Policy](https://boostcalc.com/privacy.html): Calculator inputs never leave the browser. Site uses Google AdSense; ad cookies may be set by third parties. CCPA/CPRA and GDPR opt-out mechanisms documented.
- [Terms & Disclaimer](https://boostcalc.com/terms.html): Educational tool only. Not financial, tax, legal, or accounting advice. No warranty of accuracy. Limitation of liability.

## Contact

- Email: contact@boostcalc.com
- [Contact page](https://boostcalc.com/contact.html)