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Plastiq.com is a service that will charge your credit card and mail checks on your behalf. (With some vendors they also make electronic ACH payments.)
Their usual fee for this is 2.5%. It’s worth it to incur that fee if you’re earning a signup bonus with the credit card charges, or you’re meeting a spending threshold for a bonus.
However I generally advise that it’s not worth it for the ongoing miles without a spending bonus. You don’t want to incur a 2.5% fee to earn 1 mile, you’re buying that mile at 2.5 cents. No mile is worth that.
This may be totally obvious but for business spending companies can generally write off the fee. If you’re paying business bills via Plastiq.com your net cost is 2.5% minus (2.5% * your marginal tax rate).
A sole proprietorship in the top tax bracket paying tax at the top marginal rate (and not qualifying under recent tax reform for the lower corporate rate on pass throughs) will pay a net rate around 40% in federal taxes. To that person the ‘cost’ of Plastiq is about 1.5 cents per dollar, something that can be easily worth it with a well-crafted card strategy.
Plastiq doesn’t let you use every card for each kind of charge, though. Some payment networks are persnickety about paying off a mortgage, for instance, with a credit card but is fine with paying rent.
To cut down on the confusion Plastiq created a chart to show which type of card (Visa/Mastercard/American Express/Discover/Diners) can be used for each type of payment. Red x’s are no, green checks yes. Overall American Express is more restrictive than other issuers, and you’re able to pay a residential mortgage with Mastercard credit cards, but not Visa credit cards.