Glossary

Plain-English definitions for the key terms used across our calculators.

Finance Health Maths

Finance

AER: Annual Equivalent Rate — the interest rate on savings accounts expressed as if interest were compounded once a year. Allows fair comparison between accounts that compound at different frequencies.
Amortisation: The process of paying off a debt through regular instalments over a set period. Each payment covers both interest and a portion of the principal, with the split changing over time as the balance reduces.
APR: Annual Percentage Rate — the true yearly cost of borrowing, including the interest rate plus any fees, expressed as a percentage. Used to compare loans and credit cards on a like-for-like basis.
Capital Gains Tax (CGT): A tax on the profit (gain) made when you sell an asset — such as a second property, shares, or a business — for more than you paid for it. Your main home is usually exempt.
Compound Interest: Interest calculated on both the original principal and the interest already accumulated. Over time, this causes savings (or debts) to grow exponentially rather than linearly.
Equity: The portion of a property or asset that you own outright — the market value minus any outstanding mortgage or loan secured against it.
Gross Pay: Your total earnings before any deductions such as income tax, National Insurance, or pension contributions are removed.
ISA: Individual Savings Account — a tax-efficient wrapper for savings and investments in the UK. You can save up to £20,000 per tax year (2025/26) and pay no income tax or capital gains tax on the returns.
LTV (Loan-to-Value): The ratio of a mortgage loan to the value of the property, expressed as a percentage. A £180,000 mortgage on a £200,000 property is 90% LTV. Lower LTV typically means better interest rates.
Net Pay: Your take-home pay after all deductions — income tax, National Insurance, pension contributions, and student loan repayments — have been removed from your gross pay.
Principal: The original sum of money borrowed on a loan or mortgage, before any interest is added. Over time, each repayment reduces the outstanding principal.
SDLT: Stamp Duty Land Tax — a tax paid to HMRC when purchasing a property in England or Northern Ireland above the zero-rate threshold. Scotland has LBTT and Wales has LTT instead.
Simple Interest: Interest calculated only on the original principal amount, not on accumulated interest. Less common than compound interest for savings and loans.
VAT: Value Added Tax — a consumption tax applied to most goods and services sold in the UK. The standard rate is 20%. Businesses above the £90,000 registration threshold must charge and remit VAT to HMRC.

Health

BMI: Body Mass Index — a value calculated from height and weight (kg ÷ m²) used to classify weight status. A BMI of 18.5–24.9 is considered healthy for most adults, though BMI has well-known limitations as a health indicator.
BMR: Basal Metabolic Rate — the number of calories your body burns at complete rest to maintain basic functions such as breathing, circulation, and cell production. Your BMR is the baseline for calculating daily calorie needs.
Calorie: A unit of energy. In nutrition, "calories" typically refers to kilocalories (kcal). The average adult needs roughly 2,000–2,500 kcal per day depending on size, age, sex, and activity level.
Gestational Age: How far along a pregnancy is, measured in weeks from the first day of the last menstrual period (LMP). A full-term pregnancy is 40 weeks of gestational age.
Macronutrients: The three main nutrients that provide energy: carbohydrates (4 kcal/g), protein (4 kcal/g), and fat (9 kcal/g). Tracking macros helps manage both calorie intake and nutritional balance.
Resting Heart Rate: The number of times your heart beats per minute when you are at rest. A normal resting heart rate for adults is 60–100 bpm. Athletes often have resting rates in the 40–60 bpm range.
TDEE: Total Daily Energy Expenditure — the total number of calories you burn each day, including your BMR plus all physical activity. Eating at your TDEE maintains your current weight; below it causes weight loss; above it causes weight gain.
VO2 Max: The maximum rate at which your body can consume oxygen during exercise. It is widely regarded as the best measure of cardiovascular fitness. Elite endurance athletes typically have VO2 max values above 60 mL/kg/min.

Maths

Compound Interest (Maths): Calculated using A = P(1 + r/n)^(nt), where P is the principal, r is the annual rate, n is the compounding frequency, and t is the time in years.
HCF / GCD: Highest Common Factor (also called Greatest Common Divisor) — the largest number that divides exactly into two or more numbers. For example, the HCF of 12 and 18 is 6.
LCM: Lowest Common Multiple — the smallest number that is a multiple of two or more numbers. For example, the LCM of 4 and 6 is 12.
Mean (Average): The sum of all values divided by the count of values. One of three common measures of central tendency alongside the median (middle value) and mode (most frequent value).
Percentage: A number expressed as a fraction of 100. To find X% of a number, multiply the number by X and divide by 100. To find what percentage A is of B, divide A by B and multiply by 100.
Prime Number: A whole number greater than 1 that has no positive divisors other than 1 and itself. The first ten prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29.
Quadratic Equation: An equation of the form ax² + bx + c = 0. It can be solved using the quadratic formula: x = (−b ± √(b² − 4ac)) / 2a. A quadratic always has at most two real solutions.
Scientific Notation: A way of expressing very large or very small numbers as a decimal between 1 and 10 multiplied by a power of 10. For example, 4,500,000 = 4.5 × 10⁶ and 0.00045 = 4.5 × 10⁻⁴.