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It may not make sense to prepay a 3% mortgage when you can earn 5% on a certificate of deposit, for example.

Prebooking parking at the airport does not reserve a spot but rather allows travelers to prepay for a spot and often get a savings deal compared with the drive-up price.

Forever stamps, as most first-class stamps are now designated, will always prepay one ounce of a first-class letter, regardless of future rate increases.

"For prepaying customers, when the money on the meter runs out and there's no means of topping up, so does the energy," he said.

Oracle Corp agreed to prepay $104.1 million for processor chips made by startup Ampere Computing, according to Oracle's proxy statement filed on Friday.