About the PayPal Fee Calculator
The PayPal Fee Calculator works both directions: how much lands in your account after fees, and — the reverse everyone actually needs — what to invoice so you receive an exact target amount, via gross = (net + fixed) ÷ (1 − percent). Rates are editable, since PayPal's pricing varies by account type, country and transaction and changes over time; the presets are common German merchant rates as a starting point.
Because the percentage applies to the gross you charge, fees compound: to net 100 € at 2.49% + 0.35 € you must charge 102.91 €, not 102.84 €.
Check your own PayPal fee page — goods/services, friends & family (free domestic), micropayment and cross-border all differ. Enter your exact rate above.