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Guides

Short, clear guides that explain the maths behind dates, time and percentages, with worked examples and links to the right calculator.

Guides about Guides

Illustration of a report card with grades and a weighted category pie chart October 17, 2026 · 6 min read

How to Calculate Your Grade: Weighted Average Formula with Examples

Learn how to calculate your grade with the weighted average formula: category weights, how to calculate your final…

 Illustration of a restaurant receipt showing a 20 percent tip of 9.70 dollars on a 48.50 dollar bill October 16, 2026 · 5 min read

How to Calculate Tip: 15%, 18%, 20% Guide with Examples

Learn how to calculate tip: 10%, 15%, 18% and 20% formulas, splitting the bill, and tipping customs, with worked…

 Illustration of number cards 4, 8, 6, 5, 7 with a calculator showing the average equals 6 October 16, 2026 · 7 min read

How to Calculate Average: Mean, Median & Mode Explained

Learn how to calculate average: the mean formula, median, and mode, with step-by-step worked examples and a free…

 Age calculation illustration showing 36 years 6 months 23 days with birthday cake and calendar October 15, 2026 · 8 min read

How Old Am I? How to Calculate Your Exact Age in Years, Months and Days

Learn how to calculate your exact age in years, months and days with the borrowing method. Worked examples, leap-year…

 Illustration of a scale and height tape showing a healthy BMI result of 22.9 on a category gauge October 15, 2026 · 7 min read

How to Calculate BMI: Formula, Categories & Examples

Learn the BMI formula: weight(kg) ÷ height(m)². Step-by-step metric and imperial examples, WHO categories, and a free…

 Price tag showing 25 percent discount calculation from 80 dollars to 60 dollars October 14, 2026 · 7 min read

How to Calculate Discount: Sale Price Formulas with Examples

Learn the discount formula: sale price = original × (1 − discount%). Step-by-step examples, reverse calculations, and a…

 Calendar showing whether a year has 52 or 53 weeks October 14, 2026 · 7 min read

How Many Weeks Are in a Year? 52 vs 53 Explained

A year has 52 full weeks plus 1–2 extra days. Learn when a year has 53 weeks, how ISO week numbers work, and how to…

 Clock with arrow showing how to calculate the time in X hours October 13, 2026 · 6 min read

What Time Will It Be in X Hours? How to Calculate Future Time

Add any number of hours to the current time — across AM/PM and midnight. Simple steps, worked examples, and a free…

 Pie chart illustrating how to calculate percentage October 12, 2026 · 6 min read

How to Calculate Percentage: Formulas with Examples

Learn how to calculate percentage step by step: X% of Y, percent increase and decrease, discounts and tips, with worked…

 Clock graphic showing 1,440 minutes in a day October 13, 2026 · 6 min read

How Many Minutes Are in a Day? (Plus Weeks, Months and Years)

There are 1,440 minutes in a day. Learn the simple math behind it, plus how many minutes are in a week, month and year…

 February calendar showing 29 days in a leap year October 12, 2026 · 5 min read

How Many Days Are in a Year? Leap Years Explained

A year has 365 days, or 366 in a leap year. Learn the leap year rules, why they exist, the days in each month, and…

 October 12, 2026 · 5 min read

How Many Hours Are in a Year? (Plus Work Hours in a Year)

A year has 8,760 hours (8,784 in a leap year). See work hours per year for 40, 37.5 and 35-hour weeks, minutes and…