Contact

Help make everyday math clearer.

For calculation issues, suggestions, or privacy questions, email fmfm.stars@gmail.com. PocketMath is operated by FMFM Stars / Fumiya Kobayashi in Japan.

Report a calculation issue

Small, reproducible examples are the most useful way to investigate an unexpected result. Please include:

• The tool name: tip, equal split, or sequential discount.
• The exact example inputs, including decimal places and each percentage.
• The result shown and the result you expected.
• Your browser and device type, if the problem concerns display or interaction.

For example: “Equal split: 100.00 among 3 people. I expected one share of 33.34 and two shares of 33.33, but the page showed …” You can use fictional amounts to demonstrate a problem.

Check the calculation method

The rounding guide explains why percentage adjustments are rounded before the total is calculated. The bill-splitting guide explains remainder cents, and the discount guide explains why two successive rates are not simply added together.

A merchant may round at a different stage or use a different basis for tax and tips. If a receipt disagrees, describe the arithmetic without sending a complete receipt containing personal information.

Privacy and other questions

Use the same email address for privacy questions or a request concerning a previous message. Please do not send passwords, bank details, card numbers, identity documents, or confidential account information. PocketMath does not need these details to investigate a calculation.

Clicking the email link opens your email application; it does not submit calculator entries. Information you choose to send is handled as described in the privacy notice. Response times may vary.