Damon

Posted on Mar 21

Stop Losing Money on Marketplace Fees — I Built Free Calculators for 10+ Platforms

#webdev #showdev #opensource #javascript

If you sell on eBay, Etsy, Poshmark, or TikTok Shop, you already know the pain: every platform takes a cut, and the fee structures are deliberately confusing. Some charge listing fees, others take a percentage plus a flat rate, and a few even stack payment processing on top.

I got frustrated trying to compare the real cost of selling the same item across different marketplaces. So I built a set of open-source fee calculators that break down exactly what each platform takes — no sign-ups, no ads, runs entirely in your browser.

Why Marketplace Fees Are Harder Than They Look

Take eBay: there's the final value fee (which varies by category), a per-order fee, promoted listing fees if you use ads, and PayPal/managed payments processing. Etsy layers transaction fees, payment processing fees, listing fees, and offsite ad fees. Poshmark uses a flat rate under $15 and a percentage above it.

Comparing these side by side in a spreadsheet is doable but tedious. A dedicated calculator that knows the latest fee schedule for each platform is much faster.

What I Built

Each calculator lets you input your sale price, shipping cost, and platform-specific options, then shows a detailed breakdown of every fee component plus your net profit.

CalcHub — 30 Free Calculators

E-Commerce Fee Calculators:

Finance Calculators:

Salary Inflation Calculator, Pay Raise Calculator, Freelance Tax Calculator, Compound Interest Calculator, Stripe Fee Calculator, Freelance Rate Calculator, Cost Per Hire Calculator, Credit Card Fee Calculator, Credit Card Processing Fee Calculator, Coinbase Fee Calculator, Realtor Fee Calculator, IAAI Fee Calculator, Percentage Calculator, Loan Calculator

Tech Calculators:

LLM API Cost Calculator, EV Charging Cost Calculator, 3D Printing Cost Calculator, SaaS MRR Calculator

Lifestyle:

EV vs Gas Calculator, Electricity Cost Calculator, BMI Calculator, Age Calculator, Tip Calculator

But calculators are just one part of the toolkit. I've also built specialized tool sites for developers and creators:

ToolBox Online — 22 Tools

Code formatters (JSON Escape, GraphQL Formatter, TOML Formatter, Lua Beautifier, HTML to JSX), converters (Base64, JSON to YAML, Morse Code, Hex/RGB, Pantone), generators (UUID, URL Slug, Open Graph, Random IP, Palindrome), and more.

DevToolKit — 22 Dev Tools

JSON to Zod, SVG to JSX, SQL to MongoDB, Cron Expression Generator, Nginx Config Generator, Docker Compose Generator, 5 hash generators (MD5, SHA-1/256/512, Bcrypt), JWT Decoder, Regex Tester, Chmod Calculator, and more.

ImageToolKit — 22 Image Tools

Image Resizer, Compressor, format converters (PNG/JPG/HEIC/AVIF), Circle Crop, Watermark, Instagram Grid Splitter, Photo to Coloring Page, QR Code Generator, Color Palette Extractor, Screenshot Mockup Generator, and more.

CSSKit — 15 CSS Generators

Gradient, Grid, Flexbox, Box Shadow, Clip Path, Filter, Animation, Border, Shape, Text Shadow, Transform, Transition, Background Pattern, Glassmorphism generators.

SEOKit — 15 SEO Tools

Robots.txt Generator, Meta Tag Generator, Schema Markup Generator, Open Graph Generator, Twitter Card Generator, Sitemap Generator, SERP Simulator, Keyword Density Checker, and more.

Tech Stack

All sites share the same architecture:

Next.js 16 (App Router) + React 19 + TypeScript
Tailwind CSS 4 for styling
Client-side processing — your data never leaves the browser
Deployed on Vercel

Open Source

All projects are open source:

What marketplace do you sell on, and what hidden fees have caught you off guard? I'd love to hear your stories — and if I'm missing a calculator you need, let me know!

DEV Community