Percentages without the usual traps
A 20% discount multiplies by 0.8. A rise from 80 to 100 is a 25% increase, not 20%. Sequential changes multiply; they do not always add. “Percentage points” and “percent” are different languages.
Verify with the percentage calculator. For money or grades that matter, confirm the rule written by the school, shop, or contract.
Last reviewed: 2026-09-14.
Taxes and posted prices
Whether tax is included in a sticker price changes the mental math. Apply discounts in the order the cashier’s system uses—some stack, some replace. When in doubt, compute line items the same way the receipt shows.
How this guide fits the site
Daily Toolkit pages are free browser utilities: no account is required for the basic calculators. Guides explain ideas, limits, and mistakes; tools perform the arithmetic or conversion on your device when designed that way. If an official form, bank, school, or clinician specifies a method, follow that method even when a webpage shows a different estimate.
Found an error in the explanation or a broken control on the related tool? Use the contact page with the article title, browser, and steps to reproduce. We prioritize incorrect results and unusable pages over cosmetic requests.
Limits of any single webpage
Online guides compress years of professional practice into a few screens. They cannot see your contract, your medical history, or your school’s grading rubric. When money, health, legal filings, or grades are at stake, confirm the rule with the organization that will judge the result. Use calculators here to learn the shape of a problem and to double-check arithmetic—not to replace primary documents.
We update wording when users report confusion or when a tool’s behavior changes. Dates on the page show the last editorial check, not a certification. If your browser shows an old cached copy after a site update, refresh or open a private window before reporting a mismatch between guide and tool.
Linking between guides and tools is intentional: read the explanation, run an example you already understand, then try your real inputs. If the example fails, stop and report the bug rather than trusting a larger calculation.