33 guides
Guides and Worked Examples
Step-by-step answers to the questions behind our calculators — every formula shown, every example checked.
Date & Time guides
- How to Calculate Hours Between Two TimesLearn how to calculate the hours between two times, take off a lunch break, handle night shifts and turn the result into decimal hours for your time card.
- How Much Is Time and a Half? Overtime Pay ExplainedTime and a half is 1.5 times your hourly rate. See how to figure out overtime pay, quick tables for common wages, weekly examples and the US rules.
- Dog Age Chart: Dog Years to Human YearsConvert dog years to human years with a chart for small, medium and large dogs. Learn why the 7-year rule is wrong and what a 7, 11 or 14 year old dog equals.
Finance & Loan guides
- Monthly Mortgage Payment on a $200k to $600k HouseSee the monthly mortgage payment on a $200k, $300k, $400k or $500k house with 10% or 20% down, including tax and insurance, plus how rates change it.
- How Much Income Do You Need for a Mortgage?Find the salary needed for a $250k, $300k, $400k or $500k mortgage using the 28/36 rule, with worked examples and tips to qualify for more.
- Biweekly Mortgage Payments: Do They Really Save Money?See how biweekly mortgage payments cut years and interest off a 30-year loan, how they compare with bimonthly and one extra payment a year, and the catches.
- 40-Year Mortgage: Is the Lower Payment Worth It?A 40-year mortgage lowers your monthly payment but costs far more interest. Compare a 40-year home loan with a 30-year, with real numbers, pros and cons.
- Minimum Credit Score to Buy a HouseWhat credit score do you need to buy a house? Compare minimums and down payments for FHA, conventional, VA, USDA and jumbo loans.
- Adjustable-Rate Mortgages Explained: 5/1, 7/1 and 10/1Learn how an adjustable-rate mortgage works, what 5/1, 7/1 and 10/1 mean, how rate caps protect you, and how to calculate an ARM payment after it resets.
Grade & GPA guides
- How to Calculate Cumulative GPAWhat is cumulative GPA and how is it calculated? Learn the credit-weighted method, update your GPA with this term's grades, and see what counts as a good GPA.
- GPA to Letter Grade Chart: What Is a 3.0, 3.3 or 2.5 GPA?What letter grade is a 3.0, 3.3, 3.7, 2.8 or 2.5 GPA? See a GPA to letter grade and percentage chart for the 4.0 scale, and what each GPA means for college.
- Grades Out of 20: What Is 14/20, 15/20, 16/20 or 17/20?Convert any mark out of 20 to a percentage and letter grade. Full 0-20 chart, what 15/20 or 16/20 means in the US and French systems, and how to convert.
- Percentage to Letter Grade ChartWhat letter grade is a 70, 76, 80 or 67 percent? See the full US percentage to letter grade chart, plus-minus bands, the 10-point scale and passing grades.
- How to Find the Average of NumbersLearn how to calculate an average in two easy steps, with examples for grades, decimals, negatives and percentages, plus weighted averages.
- How to Calculate Weighted Grades and Weighted GPALearn how to calculate weighted grades from category percentages, handle missing weights, and work out a weighted GPA for AP and honours classes, with examples.
- How to Calculate Your High School GPACalculate your high school GPA on the 4.0 scale step by step: convert grades or percentages to points, handle credits and find your cumulative GPA.
Health & Fitness guides
- How to Calculate Net Carbs (Keto and Atkins)Learn how to calculate net carbs for keto and Atkins: subtract fibre and sugar alcohols, avoid the UK and EU label trap, and see examples.
- How Many Calories Do 10,000 Steps Burn?See how many calories you burn per 1,000 and 10,000 steps by body weight, how to calculate calories from steps yourself, and why your tracker may disagree.
- How to Calculate Calories Burned Based on Heart RateEstimate calories burned from your heart rate with the Keytel formula for men and women, with a 30-minute chart and the limits of the method.
- BMR vs TDEE: What Is the Difference?BMR is what you burn at rest; TDEE is what you burn in a full day. Learn how to calculate your TDEE from BMR, the activity multipliers, and which one to eat by.
- How to Calculate Calories From MacrosTurn grams of protein, carbs and fat into calories, convert calories back to grams, and work out calories and macros per serving of a recipe.
Math & Science guides
- How to Calculate Percent Yield, Percent Recovery and Mass PercentLearn the percent yield, percent recovery and mass percent formulas with worked chemistry examples and how to find theoretical yield.
- How to Calculate a Discount PercentageLearn how to take a percentage off a price, find the discount percentage from two prices, handle stacked discounts and tax, with easy mental maths shortcuts.
- Percentage Difference vs Percentage ChangeLearn how to calculate the percentage difference between two numbers and the percent change, including percentage increase and decrease, with clear examples.
- How to Calculate Pool Volume (Gallons and Litres)Work out how many gallons or litres your pool holds: formulas for rectangle, round, oval and kidney pools, sloped floors and ponds.
- Square Feet to Cubic Feet and Cubic YardsLearn how to convert square feet to cubic feet and cubic yards by adding depth, convert cubic feet back to square feet, and work out mulch, soil and concrete.
- Significant Figures: Rules, Examples and PracticeSignificant figures rules for zeros, rounding, adding and multiplying, with examples like 233.356 to two sig figs and practice answers.
- Volume Formulas for Every Common ShapeEvery volume formula in one place: rectangular prism, cube, cylinder, cone, sphere, hemisphere, pyramid and prism, with worked examples and unit conversions.
- Surface Area and Lateral Area FormulasLearn the lateral area of a cone, surface area of a prism, cylinder and sphere, 2D and polygon area formulas, and cross-sectional area.
Women's Health guides
- IVF and Frozen Embryo Transfer Due DateWork out your due date after IVF or a frozen embryo transfer (FET). See the day 3, day 5 and day 6 formulas, a worked example and how far along you are.
- How to Track Ovulation With Irregular PeriodsIrregular cycles make ovulation hard to predict. Learn the calendar method, ovulation tests, temperature and mucus signs, and when to see a doctor.
Zakat & Islamic Finance guides
- How Much Is 10K, 14K, 18K and 22K Gold Worth per Gram?Work out what 10K, 14K, 18K and 22K gold is worth per gram or ounce from today's gold price, see what buyers really pay, and value white gold and jewellery.
- How to Calculate Zakat: A Step-by-Step GuideLearn how to calculate zakat on cash, gold, silver and business assets: check nisab, count the hawl, subtract debts and pay 2.5%, with full worked examples.