Calculator & Finance Glossary

Reference · 36 terms · Last updated September 2026

Every calculator assumes you know a few key terms. Here they are in plain English, grouped by field. On most tool pages on this site, underlined dotted terms show the same definitions on hover.

Loans & Borrowing

Term	Meaning
APR	Annual Percentage Rate — the yearly cost of a loan, including fees, expressed as one percentage. Lower APR usually means a cheaper loan, but compare like-for-like terms.
EMI	Equated Monthly Installment — the fixed payment a borrower makes each month. See the Loan EMI Calculator.
Principal	The original amount borrowed or invested, before any interest.
Amortization	Paying off debt through regular payments; early payments are mostly interest, later ones mostly principal.
Simple Interest	Interest calculated only on the principal: Principal × Rate × Time.
Compound Interest	Interest on interest — interest is added to the principal, so the base keeps growing. See the compound interest guide.
LTV	Loan-to-Value ratio — loan ÷ property value. Above 80% often triggers mortgage insurance.
DTI	Debt-to-Income ratio — monthly debt payments ÷ gross monthly income. Lenders use it to judge affordability.
YTM	Yield to Maturity — the total return expected if a bond is held until it matures.

Investing & Property

Term	Meaning
NPV	Net Present Value — today's value of future cash flows minus today's cost. Positive NPV generally means a project adds value.
IRR	Internal Rate of Return — the discount rate at which NPV becomes zero; handy for comparing investments.
ROI	Return on Investment — profit ÷ cost, as a percentage.
CAGR	Compound Annual Growth Rate — the smoothed yearly growth rate over a period, ignoring ups and downs in between.
Cap Rate	Capitalization Rate — net operating income ÷ property value, used to compare rental properties.

Health & Fitness

Term	Meaning
BMI	Body Mass Index — weight ÷ height², a population-level screening number, not a body-fat measurement. See the BMI guide.
BMR	Basal Metabolic Rate — calories your body burns at complete rest.
TDEE	Total Daily Energy Expenditure — BMR plus all activity; the number to match for weight maintenance.
VO2 Max	The maximum oxygen your body can use during intense exercise — a key fitness indicator.
BSA	Body Surface Area — used in medical dosing and burn assessment.

Statistics

Term	Meaning
Standard Deviation	How spread out numbers are around the mean; small = values cluster tightly.
Variance	The square of standard deviation — the average of squared differences from the mean.
Median	The middle value of sorted data; less distorted by outliers than the average.
Percentile	The value below which a given percentage of data falls — 90th percentile means 90% of values are lower.

Math Essentials

Term	Meaning
GCD	Greatest Common Divisor — the largest whole number that divides both numbers exactly.
LCM	Least Common Multiple — the smallest number both numbers divide into.
Determinant	A single number computed from a square matrix; non-zero means the matrix is invertible.
Logarithm	The inverse of exponentiation — log₂8 = 3 because 2³ = 8.
Factorial	The product of all positive integers up to n, written n! — 5! = 120.
Permutation	An arrangement where order matters (ABC ≠ CAB).
Combination	A selection where order doesn't matter (ABC = CAB).
Modulo	The remainder after division — 17 mod 5 = 2.
Complex Number	A number with real and imaginary parts, written a + bi.
Quadratic Equation	ax² + bx + c = 0, solved with the quadratic formula.
Discriminant	b² − 4ac; positive = two real roots, zero = one repeated root, negative = no real roots.
Heron's Formula	Triangle area from its three sides: √(s(s−a)(s−b)(s−c)) where s = (a+b+c)/2.
Pythagorean Theorem	In a right triangle, a² + b² = c², where c is the hypotenuse.

Using terms with the calculators

These definitions match the tooltips embedded across our tool pages. If a term on a calculator page confuses you, search this page with your browser (Ctrl+F) — each definition is written to stand on its own.