How We Calculate
Our calculators apply mathematical formulas to the information and assumptions you provide. The method varies by calculator, so check the explanation on the individual tool page.
Inputs and assumptions
Each calculator uses the fields shown on its page, which may include an amount, contribution, interest or return rate, time period, frequency, inflation assumption or target. Check units and frequency carefully. For example, an annual rate and a monthly rate are not interchangeable.
Common calculation methods
Depending on the tool, calculations may use percentage arithmetic, allocation ratios, recurring contributions, compound growth, inflation adjustments, loan amortization or savings targets. The individual calculator page should be treated as the source for the exact formula and assumptions used by that tool.
Compound growth example
A common compound-growth model is FV = P × (1 + r/n)^(n×t), where P is the starting principal, r is the annual nominal rate expressed as a decimal, n is the number of compounding periods per year and t is the number of years. This formula is an example of a standard method; not every calculator uses it, and contribution-based tools require additional cash-flow terms.
Loan payment example
For a fixed-rate, fully amortizing loan with equal periodic payments, the standard payment formula is M = P × i × (1+i)^N / ((1+i)^N − 1), where P is the loan principal, i is the interest rate per payment period and N is the total number of payments. Fees, taxes, variable rates and lender-specific rules may change actual payments.
Rounding and currency
Displayed results may be rounded for readability. Currency symbols and formatting help present the result but do not change the underlying mathematical relationship. Small differences can occur when comparing rounded figures or calculators that use different compounding, timing or rounding conventions.
Estimates and limitations
Calculator outputs are illustrations based on user-entered values, not promises or predictions. Actual outcomes can differ because of fees, taxes, changing rates, inflation, market performance, timing, product terms and individual circumstances. Investment returns are uncertain and losses are possible.
Check the individual calculator
For the most relevant explanation, read the formula, field descriptions and assumptions shown on the calculator page you are using. If you notice a possible error or unclear assumption, please contact us through the Contact page.