Methodology

Every calculator on TryClearTally is built on standard, publicly documented financial formulas — the same math used by lenders, financial institutions, and consumer finance regulators. Nothing here is a proprietary black box. This page explains the formula behind each calculator and links to authoritative sources for further reading.

Loan amortization

Used by the mortgage, auto loan, personal loan, mortgage payoff, and refinance calculators. The standard amortization formula is:

M = P × [r(1+r)ⁿ] / [(1+r)ⁿ− 1]

where M is the monthly payment, P is the loan principal, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of monthly payments. Each month, interest is charged on the remaining balance and the rest of the payment reduces principal — the same mechanics described by the Consumer Financial Protection Bureau's mortgage resources.

Compound interest & investment growth

Used by the compound interest and retirement calculators. Starting from a principal and optional monthly contribution, each month's balance earns interest at the monthly rate, then that month's contribution is added — so future contributions also start earning interest immediately. This is standard monthly-compounding math; we don't model variable returns, since no calculator can predict real market performance. The retirement calculator additionally follows employer-match conventions described in the IRS's 401(k) contribution limit guidance, though it doesn't enforce annual contribution caps — check current limits directly with the IRS if you're near them.

Credit card payoff

Each month, interest accrues on the remaining balance at the card's APR ÷ 12, your payment covers that interest first, and the rest reduces the balance — repeated until the balance reaches zero. This mirrors how card issuers calculate it; see the CFPB's credit card resources for more on how issuers calculate interest.

Savings goal

Given a target amount, current savings, an interest rate, and a timeline, we first project how much your current savings will grow on their own, then solve for the fixed monthly contribution (itself earning interest along the way) needed to close the remaining gap by your target date.

Paycheck conversion

Annual gross pay is calculated from your hourly rate, hours per week, and weeks worked per year (or directly from an annual salary), then divided into the standard US pay-period lengths: weekly (÷52), biweekly (×2 of weekly), semi-monthly (÷24), and monthly (÷12). These are gross figures, before taxes or deductions.

Live rate & market data

Where shown, default interest rates and the “Today's Rates” widget pull from the Federal Reserve Bank of St. Louis's FRED database and from Finnhub for market index and news data. This page re-fetches that same FRED data on every visit (cached for at most a day), so the figures below are live, not hand-typed:

• 30-year fixed mortgage average (MORTGAGE30US): 6.43%
• 15-year fixed mortgage average (MORTGAGE15US): 5.79%
• Effective federal funds rate (FEDFUNDS): 3.63%

Fetched July 3, 2026. See the Federal Reserve's open market operations page for how the federal funds rate is set. You can always edit any rate field on a calculator by hand.

Review process

Calculators and this page are reviewed by the TryClearTally editorial team. Each calculator shows its own “last updated” date. If you find a discrepancy between a result here and your lender's figures, it's almost always due to fees, points, or underwriting details a calculator can't see — see our financial disclaimer.