Blog
Short, practical guides on how our calculators work. Each one shows a worked example and links to the free tool.
How Does Compound Interest Work?
Compound interest explained in plain terms, with the formula and a worked example. See how interest on interest grows your money over time.
How to Calculate Sales Tax
Work out sales tax and the total with a simple formula. A clear example for adding tax to a price, plus how to pull the tax back out of a total.
How to Convert an Hourly Wage to an Annual Salary
Turn an hourly rate into a yearly figure with one formula. A worked example for full-time and part-time hours, plus how unpaid time off changes it.
How Much Water Should You Drink a Day?
A plain look at daily water needs, the common guidelines, a body-weight estimate with a worked example, and the signals that tell you how you are doing.
How to Calculate Your Target Heart Rate
Find your target heart rate zones with two clear methods, including a worked example. What the zones mean and how to measure your pulse.
What Is BMR (Basal Metabolic Rate)?
A plain explanation of basal metabolic rate: the energy your body uses at rest, the formula behind it, a worked example, and what moves the number.
How to Calculate Your GPA
Work out your grade point average on the 4.0 scale. The grade table, a worked example with credit hours, and the difference between weighted and unweighted.
The Best Time to Go to Sleep: How Sleep Cycles Work
How 90-minute sleep cycles shape a good night, plus a simple way to count back from your wake time to find a bedtime that leaves you less groggy.
How to Calculate the Days Between Two Dates
Count the days between two dates by hand with a clear month-by-month method, a worked example, and the leap-year and calendar-day details that trip people up.
How to Convert Celsius to Fahrenheit
The Celsius to Fahrenheit formula in plain terms, a worked example, the reverse conversion, and a quick mental shortcut for everyday temperatures.
How to Convert Kilograms to Pounds
The exact kilograms to pounds factor, a worked example, the reverse conversion, a mental shortcut, and the common reference points worth memorizing.
How to Convert Centimeters to Inches
The exact centimeters to inches factor, a worked example, height in feet and inches, the reverse conversion, and a mental shortcut for quick estimates.
How Much Paint Do I Need?
Work out the paint for a room by hand: measure the wall area, subtract doors and windows, account for two coats, and add a little extra. With a worked example.
How Many Tiles Do I Need?
Work out the tiles for a floor or wall by hand: find the area, convert the tile size, add a waste factor, and round up to whole boxes. With a worked example.
How Much Concrete Do I Need?
Work out concrete for a slab by hand: find the volume in cubic feet and cubic yards, convert to premix bags, and add extra for an uneven base. With a worked example.
How to Calculate a Loan Payment by Hand
Work out a fixed-rate loan payment yourself with the amortization formula. A clear, step-by-step example you can follow with a calculator.
How Is BMI Calculated?
The BMI formula in metric and imperial units, with a worked example, what the ranges mean, and the limits of what BMI can tell you.
How to Calculate a Percentage Increase
The percent change formula with everyday examples, how to handle a decrease, and the common mix-up between percent and percentage points.
How Much Mortgage Can I Afford?
The 28/36 rule, what lenders weigh, and why the maximum you qualify for is not the same as the payment you can live with.
How to Calculate Your Exact Age
Count your age in years, months, and days by hand, handle the borrowing step, and see why leap years make the math easy to get wrong.