Finance Calculator

Switch modes for loans, savings growth, and interest. Clear outputs, optional amortization preview, and Show Work.

How to Use

  1. Select a mode (Loan, Savings, or Interest).
  2. Enter values (amounts, rate, time). Choose compounding/payment frequency if applicable.
  3. Outputs update instantly (no URL changes while typing).
  4. Open “Show Work” for formulas + step-by-step math in base units.
Summary
Key results for the selected mode.
Primary
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Total / End
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Interest
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APR/APY
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Status: —
Amortization Preview (optional)

Preview shows the first few periods only (fast). Full export can be added later via JS.

Period Payment Interest Principal Balance
Enter loan details to populate preview.
Preview length and formatting controlled by the tool JS.
Inputs & Settings
Mode-driven inputs. The JS will show/hide sections and compute deterministically.
Used as principal / starting balance depending on mode.
Enter nominal APR as a percent (not decimal).
Loan length, savings horizon, or interest duration.
Payments (loan) or contribution cadence (savings).

Loan / Payment

Subtracts from amount to get financed principal.
Adds to financed principal if enabled by JS settings.
Applies extra principal each period (if supported in JS).
For estimates only (e.g., sales tax on purchase amount).
Show Work (step-by-step)
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Work is shown in consistent base units (money in USD, time in years/periods, rates in decimals inside the math).

Core Formulas

  • Loan payment (amortized): PMT = P × (i(1+i)^n) / ((1+i)^n − 1)
  • Total interest: Total = PMT×n, Interest = Total − P
  • Simple interest: I = P × r × t, FV = P + I
  • Compound growth: FV = P × (1 + r/n)^(n×t)
  • APY from APR: APY = (1 + r/n)^n − 1
Where P=principal, r=annual rate (decimal), i=periodic rate, n=number of periods, t=years.

FAQ

APR vs APY — what’s the difference?

APR is the nominal rate. APY includes compounding effects, so it’s the effective annual yield.

Why does payment change with frequency?

Frequency changes the periodic rate and number of periods. Biweekly payments often reduce total interest if you keep the same effective annual cadence.

Is this “exact to the penny”?

It’s deterministic and accurate for standard formulas. Real lenders may differ due to rounding conventions, fee timing, or exact-day interest.

Tool Info

Last updated:

Updates may include additional frequencies, export options, and improved amortization handling.