About IHaveTool

What this site is

IHaveTool is a collection of 11 free calculators across 6 categories, built for the everyday math of running an online store: profit and margins, marketplace fees, shipping and landed costs, pricing and discounts, advertising returns, and sales tax. Each tool answers one question clearly, shows the formula it used, and explains the terms involved.

The tools are meant to be used, not read. Results update as you type, every page works on a phone, and nothing requires an account, an email address, or a download.

Who builds it

IHaveTool is an independent project designed and built by Prem Thakur. It is not affiliated with Amazon, eBay, Shopify, or any carrier or marketplace named in the tools; those names are used only to describe what a calculator is for.

How the calculators are made

• Transparent formulas. Every tool has a "How is this calculated?" section that states the exact formula, so you can check the result by hand or reproduce it in a spreadsheet.
• Tested before publishing. The calculation engine behind each tool has automated tests, including edge cases such as zero quantities, percentage-based fees, and rounding.
• Your numbers, not ours. Marketplace fees, shipping rates, and tax rates change often and vary by account and location, so the tools ask you for the current figures rather than guessing.
• Private by design. All calculations run in your browser. Inputs are never sent to a server. See the privacy policy for the full picture, including analytics and advertising.

How the site is funded

The site is free and is supported by advertising served by Google AdSense. Ads are labeled as ads and never change a calculation. We do not sell data, run sponsored calculators, or accept payment to alter a formula.

Accuracy and limits

Results are estimates for informational purposes and are not financial, tax, or legal advice. If you find a mistake in a formula or a label, please tell us — corrections are the most useful feedback we receive. Read the disclaimer for details.

Get in touch

Questions, corrections, and requests for new tools are welcome on the contact page or by email at hello@ihavetool.com.