If you sell anything online, payment processing fees are silently eating your margins. A 2.9% fee sounds small until you realize that's $2,900 on every $100K in revenue — and that's before the per-transaction flat fees stack up.
I got tired of manually calculating these fees across different processors, so I built a set of free calculators that do it instantly. Here's what I learned about how each platform actually charges you.
The Real Cost Breakdown
Stripe: Simple but Adds Up
Stripe charges 2.9% + $0.30 per transaction. Clean and predictable. But if you're processing lots of small transactions (think $5-10 items), that $0.30 flat fee hits hard — you're paying 6%+ effective rate on a $5 sale.
Try it yourself: Stripe Fee Calculator
Square: In-Person vs Online Gap
Square's in-person rate (2.6% + $0.10) is competitive. But online? It jumps to 2.9% + $0.30 — same as Stripe. The real difference is Square's hardware ecosystem. If you're selling at markets or pop-ups, Square wins on convenience.
Calculate your actual costs: Square Fee Calculator
Cash App: The Hidden Instant Deposit Fee
Cash App for Business charges 2.75% per payment — no flat fee, which makes it better than Stripe for small transactions. But the trap is the 1.5% instant deposit fee (min $0.25). If you need your money fast, you're paying 4.25% total.
See the math: Cash App Fee Calculator
Venmo: The Social Payment Trap
Venmo Business charges 1.9% + $0.10 — actually the cheapest option here. But buyer adoption for business payments is lower, and Venmo's seller protections are minimal compared to Stripe or Square.
Compare: Venmo Fee Calculator
Credit Card Networks: What Your Processor Won't Tell You
Behind every Stripe/Square charge, the card networks (Visa, Mastercard, Amex) take their cut first through interchange fees. Amex charges merchants 2.5-3.5%, which is why some businesses don't accept it.
Understand the layers: Credit Card Fee Calculator | Processing Fee Calculator
Quick Comparison Table
| Processor | Rate | Best For |
|---|---|---|
| Stripe | 2.9% + $0.30 | Online SaaS, subscriptions |
| Square | 2.6% + $0.10 (in-person) | Retail, markets, pop-ups |
| Cash App | 2.75% flat | Small casual transactions |
| Venmo | 1.9% + $0.10 | Lowest rate, limited use |
| Coinbase | 0.5-4.49% | Crypto payments |
Beyond Payment Processing
These calculators are part of CalcBox — a collection of 28 free calculators I built for sellers, freelancers, and anyone dealing with fees. Some highlights:
E-Commerce Fee Calculators:
- Amazon FBA Fee Calculator — Referral + fulfillment + storage
- eBay Fee Calculator — Final value fees by category
- Etsy Fee Calculator — Listing + transaction + payment
- TikTok Shop Calculator — Commission rates
- Poshmark Fee Calculator — Commission tiers
Finance Calculators:
- Freelance Rate Calculator — Find your hourly rate
- Freelance Tax Calculator — Self-employment tax estimates
- Compound Interest Calculator — Investment growth
- Loan Calculator — Monthly payments & amortization
Tech Calculators:
- LLM API Cost Calculator — Compare GPT-4o, Claude, Gemini pricing
- SaaS MRR Calculator — MRR, ARR, LTV metrics
Everything runs 100% in your browser — no data is sent to any server. The entire project is open source: github.com/YorkeTang1993/calchub-online
What payment processor do you use, and have you ever calculated the actual percentage you're losing to fees? I was surprised how much the per-transaction flat fees matter for low-ticket items.
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