Free calculators that show their working.
Mortgage payments, loan interest, tips, sales tax, GPA, age and more. Every answer prints on a tape you can read line by line, with the formula and a worked example underneath so you can check it yourself.
- 12 calculators
- 12 guides
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- Nothing you type leaves your browser
Money & loans
Payments, interest and pay, worked out to the cent.
Mortgage Calculator
Monthly house payment with tax, insurance, PMI and HOA.
$400k · 20% down · 6.5% → $2,547.62/moLoan Calculator
Payment and total interest for auto, personal and student loans.
$25,000 · 7.9% · 60 mo → $505.71/moCompound Interest Calculator
Grow savings with monthly deposits and any compounding.
$10k + $200/mo · 7% · 20 yr → $144,572.72Salary to Hourly Calculator
Convert pay between hourly, weekly, monthly and yearly.
$62,400/yr · 40 h/wk → $30.00/hrShopping & percentages
Tips, tax and sale prices at the register.
Percentage Calculator
Percent of a number, what percent, and percent change.
15% of 240 → 36Tip Calculator
Work out the tip and split the bill between friends.
$86.40 · 20% · 3 people → $34.56 eachSales Tax Calculator
Add sales tax to a price, or take it back out.
$250 + 8.25% → $270.63Discount Calculator
Sale price with stacked coupons and sales tax.
$120 · 30% + 10% off → $75.60Dates, school & health
Ages, date spans, grades and BMI.
Age Calculator
Exact age in years, months and days, plus your next birthday.
Mar 14, 1992 → 34 yr 7 mo 7 dDays Between Dates
Count days, weeks and weekdays between two dates.
Jan 1 → Jul 4, 2026 → 184 daysGPA Calculator
Term and cumulative GPA on the 4.0 scale.
14 credits · A, B+, B, A- → 3.50BMI Calculator
Body mass index and healthy weight range for adults.
5′9″ · 165 lb → BMI 24.4Guides
How Much House Can I Afford?
A common guideline keeps your full monthly housing payment near 28% of gross income, with all debts under 36%. Here is how that turns into a home price, using clearly stated example numbers.
5 min readThe Rule of 72: How Long Does It Take to Double Your Money?
Divide 72 by an annual interest rate and you get a fast estimate of how many years it takes to double your money. Here is how accurate that shortcut is and when to use something else.
5 min readHow Much to Tip in the U.S.: Restaurants, Delivery, Hotels and More
Most U.S. tipping lands in a 15% to 20% range for personal service, with smaller or optional tips at the counter. Here are the typical ranges by service and a fast way to do the math.
5 min readHow to Raise Your GPA
How much you can raise your GPA in one semester depends mostly on how many credits you already have. The earlier you start, the more each grade counts.
5 min readHow MathTape works
The math is on the page
Each calculator lists the formula it uses and walks through a real example, so you can follow every step and check the result by hand.
Your numbers stay with you
Calculations run in your own browser. The figures you type are never sent to us or stored anywhere.
Plain-English guides
Short explainers and answers to common questions sit under every calculator, reviewed and dated so you know they're current.