I intend to donate some money to a major charity. I could donate online with a credit card, or by mail with a check. I'd like to choose the method that is less expensive for the charity, so that more of my donation can go toward their programs. But I don't have a clear sense of the costs of processing each type of transaction.
For a credit card payment, I understand the charity will have to pay a "merchant fee" to their credit card processor. I have a vague understanding that this is typically about 4% of the transacted amount, but am not sure. The card I have in mind rebates 1% of the transaction back to me, so I could increase my donation by 1% to compensate (but perhaps that card has even higher merchant fees). Also, with an online payment, I can get the receipt electronically.
For a check payment, I will incur a small expense for postage and stationary. The charity will have labor costs to open the envelope, log the payment, and take the check to the bank. Perhaps their bank also charges them to process checks, I am not sure. They will also have the expense of printing and mailing a paper receipt. I don't really have any idea how to estimate the total cost.
Since the credit card costs scale with the size of the donation, and the check costs are fixed, I assume it would be better to make small donations by credit card and large donations by check. But I don't have any idea where the break-even point is.
Data from an official source or from experience would be ideal, but even a rough estimate would be helpful.