What is here
These guides exist because a result on its own does not always tell you what you need to know. Knowing that 4% to 5% is a 25% increase is useful; knowing when to say "25%" and when to say "one percentage point" is more useful. Each guide takes one question that comes up repeatedly, answers it in the first few sentences, then works through the method with concrete numbers and lists the mistakes that cause most wrong answers.
Every guide ends with a link to the calculator it describes, so you can enter the same figures and compare. Where a guide and a tool could disagree, the guide follows the tool.
The guides
Percentage Change vs Percentage Points
You will learn why a rate moving from 4% to 5% is both "up one point" and "up 25%", and which phrasing is right in which situation. It also covers choosing a baseline, why successive percentage changes multiply instead of adding, and why a two-point move near 100% looks tiny in relative terms.
How to Add Fractions Step by Step
You will learn the five steps from unlike denominators to a reduced answer, including how to find a lowest common denominator quickly and how to handle mixed numbers and negatives. Worked sums cover 1/2 + 1/3, 3/8 + 5/12 and 2¾ + 1⅚, with the reduced fraction and the six-place decimal for each.
Tool: Fraction calculator
Image Quality vs File Size: JPG, PNG and WebP
You will learn why pixel dimensions control file size more than any quality slider does, and what lossy and lossless compression actually do to an image. It then matches formats to content — photographs, screenshots of text, logos with transparency — and explains why savings differ from one image to the next.
Why Word Counts Differ Between Tools
You will learn how hyphens, numbers, contractions and URLs change a word total, with counted examples for each. It also separates the three meanings of "character" — code units, code points and what a reader sees — using emoji and accented letters, and states the exact rule this site's counter applies.
Tools: Word and character counter, Flesch reading ease checker
How Age Is Calculated, Including Leap Days
You will learn to count age in completed years, months and days by hand, and what happens when a birth date falls on the 31st of a month that the target month does not have. It covers 29 February birthdays, notes that jurisdictions differ on the substitute date, and lists six reasons two calculators can land a day apart.
Tool: Age calculator
How a Loan EMI Is Calculated
You will learn the reducing-balance instalment formula, how to convert an annual rate into a monthly one, and how to read an amortisation schedule that starts mostly interest and ends mostly principal. It includes the zero-interest case, a term comparison from 5 to 20 years, and the costs the formula leaves out.
Tool: Loan EMI calculator
How these guides are written and checked
Every number that appears in a guide is produced by running the site's own calculation code, not typed from memory. When a guide says that 500,000 at 9% over 60 months gives an instalment of 10,379.18, that figure comes from the same function the loan calculator calls; when it says 3/8 + 5/12 is 19/24, it comes from the function behind the fraction calculator. If a tool is later changed, the guide is corrected to match it, because a worked example that disagrees with the tool is worse than no example.
Three further rules shape what you read here. Where a convention genuinely differs between countries or institutions — the substitute date for a 29 February birthday is the clearest case — the guide says so and states which rule this site applies, rather than presenting one practice as universal. Where an outcome depends on the input, as image compression savings do, the guide describes the direction of the trade-off instead of quoting a percentage from someone else's test file. And where a subject touches money or health, the guide says plainly that it is general information rather than advice.
Mistakes still get through. If a figure here does not reproduce, or a step does not work for a case we have not covered, tell us through contact and include the inputs you used, so the exact calculation can be rerun. Corrections are made to the guide and to the tool where needed. The methods and corrections page sets out the formulas, rounding rules and input limits each tool uses, and is the place to look first if a result is not what you expected.
Where to go next
Reviewed October 1, 2026. Calculation methods and corrections.