How Does Compound Interest Work?
Compound interest is interest earning interest. Here's the formula, a worked example, and why starting early beats saving more later.
Camille Laurent · 2 min read
Guides & tutorials
Practical guides, how-tos and comparisons to get the most out of our free online tools.
November 10, 2025
November 7, 2025
Percentage Change: Increase and Decrease
Subtract old from new, divide by the old value, times 100. Here's the formula, why increases and decreases aren't symmetric, and where it's used.
Lena Hoffmann · 3 min read
November 6, 2025
How to Calculate a Car Loan Payment: The Amortization Formula
Work out your monthly car payment from the loan amount, interest rate and term — plus the total interest you'll pay — using the standard amortization formula.
Camille Laurent · 4 min read
How Are Mortgage Payments Calculated?
Your monthly mortgage payment comes from three things: the amount borrowed, the interest rate and the term. Here's the formula and what moves the number.
Camille Laurent · 2 min read
November 5, 2025
What Is Your Ideal Weight?
There's no single ideal weight — it's a healthy range. Here's what the common formulas say, what they miss, and better ways to judge a healthy weight.
Sofia Nunes · 3 min read
November 4, 2025
How to Create a Strong Password
Length beats complexity. Here's why a four-word passphrase is strong, why you should never reuse a password, and how a manager makes it effortless.
Daniel Okonkwo · 3 min read
November 3, 2025
Gross vs Net Pay
Gross is what you earn; net is what you keep. Here's what comes out in between, and why you should always compare job offers on net pay.
Camille Laurent · 2 min read
How to Compress an Image Without Losing Quality
Smaller images load faster and rank better. Here's how to shrink an image the smart way — format, resolution and compression level — without visible loss.
Daniel Okonkwo · 3 min read
October 31, 2025
What Is Customer Acquisition Cost (CAC)? Formula and Benchmarks
Customer acquisition cost tells you what it really costs to win a new customer. Learn the formula, what to include, and how to read it against lifetime value.
Daniel Okonkwo · 3 min read
How Many Tiles Do You Need? (Floor and Wall)
Estimate tiles from the area to cover and one tile's size, then add for cuts and waste. Here's the method, with an example and the 10% rule.
Marco Bianchi · 3 min read
How to Calculate a Discount (and the Final Price)
A discount is a percentage off a price. Here's how to find the amount saved and the final price — plus how to stack discounts and spot fake deals.
Camille Laurent · 3 min read
October 30, 2025
How to Calculate Your Age
Subtract your birth year from this year, then take one off if your birthday hasn't come yet. Here's the rule, the common mistake, and how to get an exact age.
Lena Hoffmann · 3 min read