How Do Airline Miles Work?
Airline miles earn, expire, and redeem differently by program. Here’s exactly how the main US programs work — with real redemption numbers.
Airline miles are a loyalty currency earned by flying, credit card spending, and shopping portals. You redeem them for award flights instead of paying cash. The value per mile depends on the program and redemption — domestic economy typically yields 1–1.5 cents per mile, while international business class can yield 2–4 cents per mile when booked through partner programs. Miles from credit card welcome bonuses are the fastest way to accumulate a large balance quickly.
Miles by program — expiration rules and typical value
| Program | Miles expire after | Typical value (economy) | Typical value (intl biz) |
|---|---|---|---|
| Delta SkyMiles | Never | ~1.1–1.2c | ~1.2–1.8c |
| United MileagePlus | 18 months inactivity | ~1.2–1.4c | ~1.5–2.0c |
| American AAdvantage | 24 months inactivity | ~1.1–1.3c | ~1.4–2.0c |
| Southwest Rapid Rewards | 24 months inactivity | ~1.4–1.6c | Domestic/Caribbean only |
| Air France Flying Blue | 24 months inactivity | ~1.3c | ~1.8–2.5c |
| Air Canada Aeroplan | 12 months inactivity | ~1.3c | ~1.8–2.5c |
| British Airways Avios | 36 months inactivity | ~1.1c (varies by distance) | ~2.0c+ on partner carriers |
Values are estimates based on typical redemptions. Actual CPP varies by route, cabin, date, and availability. No affiliate relationship with any program listed.
How to earn miles without flying
- Credit card welcome bonuses — 50,000–80,000 miles after meeting a spending requirement. This is the fastest single source of miles for most people. See the best signup bonuses →
- Transferable points programs — Chase Ultimate Rewards transfers to United and Southwest at 1:1; Amex Membership Rewards transfers to Delta and Air Canada Aeroplan. Using a Chase Sapphire card means you can send points to whichever airline has the best availability when you need to book. Prefer no annual fee? The best no-fee travel cards still earn transferable points.
- Credit card everyday spending — Co-branded airline cards typically earn 1–3 miles per dollar on the airline, 1–2x on dining and gas, and 1x on everything else.
- Airline shopping portals — Most major airlines have shopping portals (Delta SkyMiles Shopping, United MileagePlus Shopping) paying 2–10x miles on purchases from major retailers.
- Dining programs — United, American, and Delta dining programs pay 2–5 miles per dollar at enrolled restaurants, with a bonus for the first restaurant visit.
- Hotel transfers — Marriott Bonvoy transfers to most airline programs at 3:1 (60,000 Bonvoy = 20,000 airline miles) with a 5,000-mile bonus at 60,000 transferred.
When miles are NOT worth redeeming
Miles are worth less than their average value when redeemed for merchandise, gift cards, or statement credits — typically yielding 0.5–0.8 cents per mile, well below the 1–2c average for flights.
Delta SkyMiles specific: Delta uses dynamic pricing, meaning award costs fluctuate based on demand. On high-demand routes or dates, Delta may charge 30,000–50,000 miles for a flight that costs the same in cash as a route priced at 8,000 miles during off-peak periods. Always compare the cash price before redeeming.
The cents-per-point test: Divide the cash price of the flight by the miles required. If the result is less than 1.0c per mile, paying cash is better. Use the Trip Gap Calculator to run this comparison for any trip — or plug your spending into the rewards calculator to find the best card for your earning profile.