Depends on your details. Absolutely minimum for me would be 30 minutes (assuming you have PreCheck, PreCheck is open, you have checked in online and no checked bags).

Add more time as needed

1. Safety margin for mental comfort
2. Average wait time at TSA (if you don't have PreCheck or Clear): https://www.tsawaittimes.com/security-wait-times/SEA/Seattle-Tacoma-International
3. Unusual items in your carry on
4. Checked baggage, visit to check in counter (depending on status)

Personally I shoot for 1 hour on domestic flights and that has always worked.

Officially SeaTac suggests arriving at least 2 hours early

IMO these recommendations are male bovine fecal matter. On a recent international departure I arrived early (I had lounge access and wanted to get some work done). Recommended arrival time was 3 hours before departure but the check in counter only opened 2 hours before, so there was a huge line of people standing in front of the closed counter.

Depends on your details. Absolutely minimum for me would be 30 minutes (assuming you have PreCheck, PreCheck is open, you have checked in online and no checked bags).

Add more time as needed

1. Safety margin for mental comfort
2. Average wait time at TSA (if you don't have PreCheck or Clear): https://www.tsawaittimes.com/security-wait-times/SEA/Seattle-Tacoma-International
3. Unusual items in your carry on
4. Checked baggage, visit to check in counter (depending on status)

Personally I shoot for 1 hour on domestic flights and that has always worked.

Officially SeaTac suggests arriving at least 2 hours early

IMO these recommendations are not worth the paper they're written on. On a recent international departure I arrived early (I had lounge access and wanted to get some work done). Recommended arrival time was 3 hours before departure but the check in counter only opened 2 hours before, so there was a huge line of people standing in front of the closed counter.