Percentage calculator solves five common questions: what X% of a number is, what percent one number is of another, the percentage change between two values, and the result of adding or subtracting a percentage, such as a discount or a raise. Its tax mode adds sales tax or VAT to a price or removes it from a total, with the standard rates of several countries or any rate you type; in the United States the rate depends on the state and city, so you enter your local rate. The VAT calculator page opens directly in that mode, ready for invoices, quotes and receipts.
Date calculator counts the days between two dates, adds or subtracts days from a date, counts business days without weekends and, optionally, without the national holidays of 2026 and 2027 for nine countries including the United States, and gives an exact age in years, months and days. Two pages start in a specific mode: Business days calculator for delivery times and payment terms, and Age calculator for forms, school enrollment and a baby's age in months.
Grade calculator works out a simple or weighted average with any scale, from 0–4 to 0–100, and tells you what grade you need on the rest of the course to reach a target, or warns you when even a perfect score won't be enough. It is the tool to check where you stand before a final exam or at the end of a semester.
Compound interest calculator simulates how savings grow with an initial amount, a monthly contribution, an annual rate and monthly or yearly compounding, and shows a year-by-year table. It uses a fixed rate and leaves out taxes, fees and inflation, so treat it as a way to understand the math and compare scenarios, not as investment advice.
A related tool lives in the text section: Number to words writes an amount in words for checks, invoices and contracts, a natural next step after working out a total with tax. All calculators are free, with no account and no usage limit, on phones and computers.