What each tool does
Loan & Mortgage Calculator
Monthly payment on a fixed-rate loan = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the amount borrowed, r is the monthly interest rate and n is the number of months. A $300,000 mortgage at 6.5% for 30 years costs $1,896.20 a month, with $382,633 paid in interest over the term.
Compound Interest Calculator
Compound interest uses A = P(1 + r/n)^(nt), where P is the starting amount, r the annual rate, n the compounding periods per year and t the years. $10,000 at 7% compounded monthly grows to about $40,387 in 20 years. The rule of 72 says money doubles in roughly 72 ÷ rate years.
Sales Tax, VAT & GST Calculator
To add tax, multiply the net price by (1 + rate). To remove tax from a total, divide by (1 + rate): £120 including 20% VAT is £100 + £20 VAT. UK VAT is 20% standard and 5% reduced. India GST since 22 September 2025 uses 5% and 18% with a 40% rate for luxury and sin goods, split equally into CGST and SGST within a state. US sales tax is set by each state and locality.
Discount Calculator
To find a sale price, multiply the original price by (1 − discount ÷ 100). A $80 item at 25% off costs $80 × 0.75 = $60, saving $20. Two discounts are applied one after the other, so 20% off and then 10% off equals 28% off, not 30%.
Tip Calculator
To work out a tip, multiply the bill by the tip percentage. A 20% tip on a $64 bill is $12.80, making $76.80. Divide by the number of people to split it. In the US 15–20% is usual at sit-down restaurants; in the UK 10–12.5% is common and is often added as a service charge.
Salary Calculator
To convert an hourly wage to a yearly salary, multiply it by hours per week and then by weeks worked per year. At 40 hours a week for 52 weeks, that is 2,080 hours, so $20 an hour is $41,600 a year before tax. To go from salary to hourly, divide by the same number of hours.
Profit Margin Calculator
Profit margin is profit divided by selling price; markup is profit divided by cost. If an item costs 60 and sells for 100, profit is 40, margin is 40% and markup is 66.7%. To price for a target margin, divide cost by (1 − margin): a 60 cost at 40% margin needs a price of 100.