Airline miles

Try booking one way at a time, one with each airline program.

As suggested above by Lola, try to use one bucket of points for the outbound flight, and the other bucket of points for the return - that's usually the only reasonable option.

Generally speaking, you usually can not "combine" points from one airline/company program with another (the miles/points are in a "loyalty program" - the whole reason for these programs is to attempt to make you "loyal" to that company). There are a few exceptions/loopholes/workarounds, but those tend to be wonky/edge cases, a very bad deal, or just unworkable in most cases.

What programs are your points in?

I also use the one way option on American and United.

Hi. I don’t know your points situation, but you may want to take a look at Flying Blue (KLM, Air France etc.). I was able to transfer pts from multiple programs to Flying Blue. Chase, Cap One, Citi Thank You Pts, Marriott and Amex MR all transfer to Flying Blue.

When traveling from US to Europe, I have found that booking one way is very expensive compared to booking round trip.

Maybe the situation will be different to and from Ireland.

I book one-way tickets from the US to Europe every summer, only in economy, and only for the fewest number of miles. United and American make this easy and inexpensive, but I only recently discovered that Delta no longer allows you to do so for half the fare of a round trip.

We flew to France last summer with Delta miles and home from London with American.

I don’t know when the policy changed; I do plan way ahead.

ScandiFan--We came across that with Delta this fall, aroundSeptember or so. Even the Delta agent on the phone was surprised by it.

Sometimes it depends on the partner airline whether a one way costs the same as roundtrip, even within the same airline alliance. It pays to price both ways to know how it works for that particular airline.

Example: British Airways, I can buy one way for half of round trip. Korean Airlines, it will cost me the same number of miles whether I book one way or round trip. This is all within the same mileage program.

Paying with money, then rwo one-ways can be more expensive than round trip. But with miles that is not the case.

As mentioned, simply book over with one airline and back with the other. I’ve done it several times

I have United miles and I can and have booked one way tickets. The number of miles does not increase doing it this way.

Booking award seats with miles is different from booking revenue seats with cash and points, and different rules apply. Airlines limit the number of award seats available on each flight, and when those are booked, the flight is no longer available with miles. Or, as with American Airlines, the “cost” in number of miles goes way up.

I use British Airways Avios and Alaska Airlines miles, and always book one way at a time, for half the number of miles as a roundtrip. Airlines I have booked this way include BA to Europe, American to South America, Qantas to Australia (in First Class!) , and Japan airlines to Tokyo. All airlines are in the One World partner group.

Booking one way at a time gives you much more flexibility.. I can book the outbound trip when the award seats are first released, rather than waiting for the return flight seats to be released. By that time, the outbound seats are likely gone. British Airways, for example, releases 2-4 award seats in Business Class on each flight 355 days in advance. They are usually taken that day, so anyone who waits until a later date to book round-trip may be out of luck.

I do this all the time!
I have a plethora of miles on both American and United airlines.
Even using miles, American Airlines code share with BA passing through London Heathrow elicits a hefty surcharge, as high as 7-900$ . This is a London Heathrow thing and inescapable.
But I can get around that by using my United airlines miles on the outbound.
And oddly the return using AA miles the London Heathrow charge is usually in the 2-300$ range.
All the above relates to business or first class which is when I use my miles.
I would never have been able to buy business class to Europe so I'm grateful for figuring out how to maximize the opportunity!

@cafetieta - I have been able to book business class to Europe on AA 3 times ( 2 of which I had to cancel because of Covid ). Each time I found that the miles required varied by almost a factor of. 2, depending on the day I looked online - for the same flight !!

I switched from using miles JFK-LHR and return from British Airways to American Airlines. Business class. My "fees" dropped about $800 roundtrip.

Heathrow is not the issue. British Airways is the problem.

With which two different airlines do you have points?

In general, though, just book one way flights with the two different airline points.