Originally Posted by
TerryK
The vast majority of round-trip fares within North America are the same as two one-ways. There could be minor differences, like a few dollars, due to taxes. In those cases, half the fare paid is the same as, or very close to, the round-trip fare minus the one-way fare.
The OP's case is round-trip is less than one one-way.
I wouldn't necessarily say "vast" majority. If you live in a competitive market like NYC, it's mostly true. But if you are based in a smaller market or captive market like DTW, the majority of DL domestic routes still have roundtrip fares which are cheaper than buying two one-ways. Although the pricing difference is generally not so steep that a one-way fare costs more than a roundtrip (differences are frequently only in the tens of dollars each way for domestic fares) and most people probably don't really notice them. If you do any fare searching on ExpertFlyer, the roundtrip fares are rather obvious as they have a value in the minimum stay column while the one-way fares do not.
As an example, the current cheapest DL one-way fares on DTW-LAX are $299, while the cheapest roundtrip fares on route are $249 each-way.