Guides

Short, practical explanations of the calculations behind our tools. Each guide starts with a direct answer, then shows the formula, a step-by-step method and worked examples you can check by hand.

Math & money

GuideHow to Calculate PercentageLearn the three percentage formulas: finding a percent of a number, what percent one number is of another, and percentage change.Read guide
GuideHow to Calculate a DiscountWork out a sale price from a percentage off, find the discount rate from two prices, and see why stacked discounts don't simply add up.Read guide
GuideHow to Calculate Simple InterestSimple interest explained with the I = P × R × T formula, converting months and days to years, and how it compares with compound interest.Read guide
GuideHow Compound Interest WorksThe compound interest formula explained, how compounding frequency changes growth, and how regular contributions add up over time.Read guide
GuideHow to Calculate a Loan PaymentUse the amortization formula to calculate fixed loan payments, understand how each payment splits into interest and principal, and compare terms.Read guide

School & university

Health

Everyday

About our guides

Who writes these guides?

The guides are written and reviewed by the Toolvix team. Each one explains the standard formula, walks through examples with the numbers shown, and links to a calculator that does the same arithmetic.

Can I use the formulas for homework or work?

Yes. The formulas are the standard ones taught in schools and used in finance and health. For graded work or official figures, follow the exact method your teacher, school or provider specifies.

Why do some guides include a disclaimer?

Health and finance results depend on personal circumstances, so those guides explain the general method and recommend confirming decisions with a qualified professional or your lender.