Calculator Guides

Short, practical guides that explain the maths behind each calculator, with worked examples you can check yourself. Pick a topic, learn the method, then open the matching calculator to try your own numbers.

• How to Calculate Percentages: Simple MethodsLearn the three core percentage calculations, how to reverse a percentage, and the difference between percent and percentage points, with worked examples.
• Discount Guide: Sale Prices and Stacked DealsWork out sale prices, check a price tag, find the original price, and see why 20% off then 10% off is not 30% off. Worked examples included.
• Percent Change: Increase, Decrease and GrowthHow to calculate percent increase and decrease, why +10% then -10% does not get you back to the start, and how to read growth rates in charts.
• How Age Is Calculated: Years, Months and DaysSee how age is counted in completed years, how to get exact years, months and days, how February 29 births work, and why traditions differ.
• Days Between Dates: Counting, Adding and CountdownsHow to count the days between two dates, inclusive versus exclusive counting, adding days to a date, leap years and month lengths, with examples.
• Time Calculation Guide: Hours, Minutes, DifferencesFind the time difference across midnight, convert minutes to decimal hours, add hours and minutes, and plan trips or study sessions without mistakes.
• Fractions: Add, Subtract, Multiply and DivideStep-by-step methods for adding, subtracting, multiplying and dividing fractions, plus simplifying, mixed numbers and converting to decimals.
• Scientific Calculator Guide: Angles, Powers, E NotationUse a scientific calculator correctly: degrees versus radians, order of operations, powers, roots, logs, factorials and scientific notation like 6.674E-11.
• Order of Operations: PEMDAS, BODMAS and 8÷2(2+2)Why 2 + 3 × 4 is 14, how left-to-right rules work, why 8÷2(2+2) goes viral, and why a phone calculator can disagree with a formula calculator.
• Rounding Numbers: Decimal Places and Significant FiguresRound to decimal places or significant figures, round up or down, handle negative numbers, and see why 0.1 + 0.2 shows 0.30000000000000004.
• Averages Explained: Mean, Weighted Average, Median, ModeCalculate a mean and a weighted average, choose between mean, median and mode, avoid the average-of-averages trap, and find the score you need next.
• Ratios and Proportions: Recipes, Maps and Fair SplitsSimplify ratios, solve proportions by cross-multiplication, scale a recipe, read a map scale, turn ratios into percentages and split amounts 3:2.
• Leap Years, Month Lengths and Finding the WeekdayThe 4/100/400 leap year rule and why it exists, February 29 birthdays, days in each month, and a simple method to find the weekday of any date.
• Decimal Hours, Minutes and the 12/24-Hour ClockConvert 1.75 hours to 1 h 45 min and back, turn seconds into minutes, switch between 12-hour and 24-hour times, and add up several durations.
• Fractions, Decimals and Percents: Converting Between ThemConvert fractions to decimals and percents, see which fractions terminate and which repeat, and turn repeating decimals like 0.1666... back into fractions.
• Logarithms Made Simple: log, ln and Real-World ScalesWhat a logarithm means, log10 versus ln, the log rules, change of base, and how logs work in earthquake magnitudes, decibels, pH and doubling time.