Should I buy these miles?
Airlines sell miles, often with a bonus, and whether that is a good deal is one of the few questions here with a real answer. Enter what the miles cost and the award you would use them for, and this compares the two.
Answer
Fill in the offer and the award you would book. Nothing you type leaves your browser.
How this is worked out
Two numbers, compared:
cost of the miles ÷ miles bought × 100 = cents per mile to buy
(cash price − award fees) ÷ miles required × 100 = cents per mile released
If the second number is bigger than the first, the miles release more cash than they cost, and buying wins on that booking. If it is smaller, you are paying money to lose money. The bonus percentage, how good the offer sounds and how rarely it comes around are all noise beside that comparison.
A worked example
An airline offers 60,000 miles for $1,200.00. You have found a business-class seat selling for $2,500.00 that the same airline will sell as an award for the same 60,000 miles plus $60.00.
$1,200.00 ÷ 60,000 miles × 100 = 2.00¢ per mile to buy, against 4.07¢ per mile released by this award
Buying the miles and booking the award would cost you $1,260.00 in cash, against $2,500.00 to buy the ticket outright - a difference of $1,240.00. Each mile costs 2.00 cents and releases 4.07 cents of airfare.
That is the shape of a purchase worth making: the miles cost about half what they release. Note how much work the phrase “you have found a seat” is doing — without a confirmed award this whole calculation is hypothetical.
The two ways this goes wrong
Buying on the offer rather than the booking. A promotion that makes miles cheap does not make them useful. Miles bought without a specific award are cash converted into an asset the seller prices, can devalue, and will not refund. That is the single most expensive habit in this corner of the hobby.
Valuing the award against a fare you would never pay. If you would not have bought the $2,500.00 business-class ticket, then buying miles to sit in it is not saving you $1,240.00 — it is spending real money to upgrade a trip you would have taken in economy. That can be a perfectly good decision, but it is a different one, and the arithmetic will not tell you which you are making.
Our explainer on where outsized value comes from covers why some awards release far more than others, which is what makes a purchase like this possible at all.
Questions people ask
Is buying miles ever a good idea?
Sometimes, and only against a specific award you have already found and priced. The test is simple: if a mile costs you less to buy than the cash it releases on that booking, buying wins. If it costs more, you are paying money to lose money. Everything else - the bonus percentage, how good the offer sounds, how rarely it comes around - is noise next to that comparison.
Why does buying speculatively go wrong so often?
Because you are paying real cash for an asset whose price the seller controls and has a standing incentive to raise. A promotion that makes miles cheap does not make them useful. Without a booking in mind you have converted money into something that can be devalued, cannot be refunded, and may never buy the thing you imagined.
What if I already have some of the miles?
The calculator handles it, but read the warning it produces. Comparing only your cash out of pocket flatters the deal, because the miles you already hold are being spent too and could have funded a different trip. The dollar saving is real; it just is not the whole story.
How big a margin should I want?
Bigger than you think. This is a non-refundable purchase against a seat that can disappear between buying and booking. A result that only just beats the cash fare does not leave room for anything to go wrong, which is why we flag thin margins rather than calling them a win.
Does a bigger bonus make an offer better?
Not by itself. A 100% bonus on expensive miles can still be worse than no bonus on cheap ones. Work out the all-in cost per mile after the bonus and compare that against what the award releases - that is the only number that decides it.