popo, welcome!

As azmmza says, the cost for your upgrade in miles should be 25,000 miles each way, up to three segments included. LGW - DFW - SEA would definitely be covered outbound from the UK, as well as ATL - DFW - LGW return; I think the SEA - ATL could have to be "paid" for by upgrades, but I may be wrong, it may be included in the original 25,000 each way.

If the international leg doesn't clear, BTW, I'd try upgrading with domestic upgrades and save my miles for future travel.

I'm sure others will post more extensively and knowledgeably about this SEA - ATL leg; I assume you will be stopping off both in SEA and in ATL?

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