I noticed a lot of sellers, who use PayPal, tell their buyers to add 3% to the cost.
After reading the PayPal link below, I noticed this method is not entirely correct. So, I developed a very simple equation with the intention to help.
This equation works for most transactions, more info here: https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=marketing_us/fees
Round up to the nearest penny, two decimal places or hundredths place if necessary.
Useful when the seller has a set price and needs to find how much the buyer will be required to pay.
Buyer's Cost = ((Seller's Price + Shipping) * 1.029) + 0.3
Useful when the seller has an offer from a buyer and needs to find how much he will receive.
Money Received by Seller = ((Buyer's Offer - 0.3) / 1.029) - Shipping