Reader Vicky S. of Stockton, California writes in:

I’m flying to New York in September on United, and I’m wondering if there is any way for me to use my Capital One miles to upgrade. I have over 20000 miles with the card.

Vicky, I’m afraid you’re out of luck. You would need United Mileage Plus miles or upgrade certificates to upgrade the flight. Too bad, too, because upgrading on the cross-country flights to JFK, in United’s three-class planes, is worth it.

You can use those CapitalOne miles to buy a ticket, but you can’t use them for upgrades on any airline. That’s one of the tradeoffs that comes with credit card miles that aren’t linked to a specific carrier.

As a general rule, I’m opposed to bank-issued miles, like CapitalOne’s “No Hassle Rewards,” as opposed to airline-issued miles. Sure, you get to cash the bank’s miles in for any airline’s ticket, but that really just means you’re getting cash back. Why not get a card that actually pays you in real cash, then?

Besides, the value of those bank-miles isn’t that great. CapitalOne sets cutoffs for redemption of their miles:

15,000 miles are required for tickets up to $150; 35,000 miles are required for tickets from $150.01 up to $350; 60,000 miles are required for tickets from $350.01 up to $600. For tickets over $600 in value, the required number of miles will be determined by multiplying the cost of the ticket times 100 (ex. $768 ticket requires 76,800 miles).

That means you’re getting 1 cent per mile MAXIMUM, with ZERO chance of leveraging those miles for an upgrade (like you just discovered) or a premium-cabin ticket. A business class ticket to Australia could easily run you $8000 — which would require 90,000 United Mileage Plus miles (though that’s going up to 110,000 miles in October) or a whopping 800,000 CapitalOne miles.

So for now, check your United account to see if you have enough miles for the upgrade. It’ll most likely cost you 15,000 United miles each way.