Calculators with visible methods and practical assumptions
A useful calculation starts with the right question and units. These tools show results for the values you supply; they do not choose a tax rate, lending agreement or medical interpretation for you.
Choose by the task
- Everyday amounts: percentages, discounts, tips and VAT.
- Financial scenarios: fixed-rate loan payments or compound growth with explicit assumptions.
- Calendar dates: age and elapsed differences. Adult BMI interpretation is for ages 20 and older.
Everyday amounts
Percentage Calculator
Calculate percentages, proportions, and percentage change with safe handling for zero denominators.
Discount Calculator
Calculate savings, discounted price, optional tax, and final price.
Tip Calculator
Calculate a tip, total bill, and per-person split.
VAT Calculator
Add VAT to a net amount or remove VAT correctly from a gross amount.
Financial scenarios
Health, dates and numbers
BMI Calculator
Calculate adult body mass index using metric or imperial measurements.
Age Calculator
Find calendar age in completed years, months, and days for a chosen date.
Date Difference Calculator
Compare two calendar dates in days, weeks, months, and years without timezone drift.
Average Calculator
Find the mean, sum, count, minimum, and maximum of a number list.
Separate a rate from the amount it applies to
Percent-of, percentage change, discounts, tips and VAT use different bases. Removing included VAT is division by one plus the rate, not subtracting the same percentage from the gross price. A discount followed by tax applies the second rate to the reduced amount.
Read the result labels and keep full precision until the final step where possible. Rounded per-person bills can need a small adjustment when collecting an exact total.
Use projections as scenarios
Loan payments model a fixed-rate monthly amortization schedule. Compound interest models specified growth and contributions. Neither includes every fee, tax or variable rate in a real financial product. Compare assumptions with the actual agreement before relying on an estimate.
BMI is an adult screening calculation, not a health diagnosis. Age and date difference use calendar logic; they do not provide a legal deadline or a business-day calendar. The average tool summarizes the numbers entered, not a statistically representative sample by itself.
Questions about this topic
Why does a calculator result differ from an official quote?
The quote may include fees, date conventions, rounding or a different rate basis. Compare inputs and assumptions before treating a mathematical difference as an error.