This is a complete, single-file "Free Online Marketplace Seller Fees and Profit Margin Calculator" application. It uses modern web standards, Tailwind CSS for the SaaS aesthetic, and Vanilla JavaScript for instant, real-time calculations. You can save the code below as an `.html` file and open it in any modern browser. ```html Free Online Marketplace Seller Fees and Profit Margin Calculator

Marketplace Fees & Profit Calculator

Instantly analyze your net profit and break down platform fees.

Revenue

Sale Price ($)

Shipping Charged ($)

Costs

Production ($)

Shipping Cost ($)

Misc Fees ($)

Platform Fees

Listing Fee ($)

Transaction (%)

Processing (%)

Fixed Fee ($)

Financial Summary

Net Profit

$0.00

Margin

0.0%

Revenue

$0.00

Total Fees $0.00

Total Costs $0.00