How we calculate.

Standard formulas, shown in the open

Each calculator uses the textbook definition of its metric — the same formulas found in finance courses, lender documents, and professional underwriting. Rental yield, cap rate, and cash-on-cash return are ratios of income to price or cash invested; mortgage payments use the standard fixed-rate amortization formula; CAGR, annualized ROI, and real returns use compound growth and the Fisher equation; bond yield to maturity is solved numerically from the bond pricing equation. The exact formula is printed on every calculator page, directly under the result.

Every result comes from your inputs

There are no hidden variables, market data feeds, or adjustments. If a result changes, it is because an input changed. Default values are realistic examples chosen to make the page useful immediately; they are not recommendations or forecasts, and you should replace them with your own numbers.

Assumptions we make, and say so

Projections apply the growth, inflation, and appreciation rates you enter as constant yearly rates. Real markets do not move in straight lines, so projections show the shape of your assumptions, not a prediction. Compound interest is calculated monthly; mortgage and loan figures assume a fixed rate and monthly payments; bond coupons are paid at the frequency you choose. Taxes are not modeled unless a calculator says otherwise, because they depend on your personal situation.

Currency switching uses fixed, illustrative exchange rates so that example amounts look sensible in each currency. They are not live rates, and they never affect the math: every calculation runs on the numbers in the input fields.

How the calculators are tested

The calculation logic is kept separate from the page design and covered by automated tests. Each formula is checked against values worked out independently by hand — for example, a $320,000 mortgage at 6.5% over 30 years must come to $2,022.62 a month — along with edge cases such as zero interest, zero years, and negative returns. The tests run every time the site is built, so a change that breaks a formula cannot be published.

How articles are written

The articles in the Learn section explain what each metric measures and where it misleads. Worked examples are checked against the same formulas the calculators use, so the numbers in the text match what you will see when you enter them. Each article shows the date it was published and last updated.

Corrections

If you find a result or an explanation that looks wrong, please email us. We check every report, fix confirmed errors promptly, and update the date on the affected page.

What this site is not

The calculators illustrate standard formulas; they do not know your full financial situation and are not financial, tax, or investment advice. See the disclaimer for the full picture.