Top-ups are the simplest use case
Buying a small number of miles can make sense when an account is just short of a confirmed award and the incremental purchase is cheaper than another way of earning the difference.
Large speculative purchases carry more risk
Programs can change award prices, availability rules or partner access. Buying a large balance without an immediate use exposes the traveler to that devaluation risk.
Promotional bonuses change the effective price
A 50 or 100 percent purchase bonus lowers the cost per mile, but the advertised bonus should still be compared with the actual value of the intended award.
Taxes and surcharges belong in the calculation
The true cost of an award is purchased miles plus any remaining taxes and carrier fees. Ignoring the cash component can make a redemption look better than it is.
Purchase limits can restrict the strategy
Programs often cap annual mileage purchases or apply different pricing to gifts, transfers and self-purchases. Account age or prior activity can also affect eligibility.
Compare against the cash ticket first
If the same trip is inexpensive in cash, buying miles rarely creates value. The stronger cases tend to involve otherwise expensive premium seats or a small top-up for scarce inventory.
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