CALCSLIP

Calculate anything. Instantly.

Free calculators for money, dates, math and everyday numbers. The answer appears as you type, with the formula and every step written out.

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Mortgage · $400,000 home, 20% down

Monthly payment
$2,547.62
Principal & interest
$2,022.62
Property tax
$400.00
Home insurance
$125.00
Loan amount
$320,000.00
Total interest
$408,140.64
Interest rate
6.5%
Term
30 years
The result tape from the mortgage calculator. Every line can be copied, shared as a link, or pinned and compared.
The scales of a 1967 Faber-Castell slide rule, with its glass cursor
A 1967 Faber-Castell slide rule: logarithms you could hold.

20 calculators, one way of working

Finance

Date & time

Math

Everyday

Pin a result. Compare the next.

Pin a result and it stays on the tape while you try another: a shorter term, a bigger deposit, a different rate. Every line shows what moved and by how much, in green when it helps you and red when it costs you.

Here a 15-year loan at 5.875% is set against the 30-year loan at 6.5%. The monthly payment rises by $656.16, and the total interest falls by $245,960.46.

Try it in the mortgage calculator

15 years, compared with 30 years

Monthly payment
$3,203.78+$656.16
Principal & interest
$2,678.78+$656.16
Total interest
$162,180.18−$245,960.46
Paid off
15 years sooner−180 payments

Compared with the pinned result ($2,547.62).

The working, not just the answer

  1. Monthly interest rate

    r = annual rate ÷ 12

    6.5% ÷ 12 = 0.00541667

  2. Principal and interest

    M = P × r ÷ (1 − (1 + r)^−n)

    $320,000.00 × 0.00541667 ÷ (1 − 1.00541667^−360) = $2,022.62

  • Your numbers in the formula

    Each step prints the formula, then the same formula with your own figures in it, so you can check it by hand or in a spreadsheet.

  • Assumptions said out loud

    When payments are due, how often interest compounds, when PMI stops, what is left out. Written under every result, not hidden in a footnote.

  • Type the way you think

    Every number field takes 250k, 1.2m, $1,500 or 1200*12. The figure it reads is shown under the field.

  • A link that reopens the calculation

    Inputs live in the page address. Share it, bookmark it, or come back to it; no account, nothing stored on a server.

How CALCSLIP checks its formulas

Adding machines showed their sums

For a century, office calculators printed every entry and every total on a roll of paper, so anyone could check the sum line by line. CALCSLIP keeps that habit: the result is a tape you can read, copy and hand to someone else.

A beige Odhner 200 pinwheel calculator seen from above, with its crank handles and number wheels
Odhner 200 pinwheel calculator, made 1955–1967.
A black Corona portable adding machine with columns of white and black number keys
Corona portable adding machine, Polytechnic Museum, Moscow.
A worn black Triumph adding machine with sliding number columns, patented 1907
Triumph adding machine, patented 1907.
The opened mechanism of a Remington adding machine with its paper roll and plus key
Remington Model 102, with its paper roll at the back.

Pictures from Wikimedia Commons: slide rule by R. Henrik Nilsson, CC BY 4.0; Odhner 200 by Daderot, CC0; Corona by Александр Сигачёв, CC0; Triumph by Gnangarra, CC BY 3.0; Remington 102 by Issac I Navarro, CC BY 4.0.