USCG course certificates are valid for 1 year domestically and 5 years for STCW. Check the date on your certificate for specifics.
Approved courses for domestic USCG licenses are valid for one (1) year after the issue date.
International STCW endorsements are valid for 5 years.

This comes from 46 CFR § 11.201 - General requirements for national and STCW officer endorsements.
The best place to look for your course expiration date is on the course approval information on your course certificate. It will typically say "must be submitted within one (1) year of the date shown" or "must be submitted within five (5) years of the date shown".
Any course certificate or training related to a 6 pack, 100 ton Master or 200 ton Master will need to be submitted within one (1) year.

We hope this made your life a little easier and if you have other questions the MM-SEAS team is always here to help!
MM-SEAS is free to use on your own and if you need some more personalized help you can upgrade to MM-SEAS Expert Access inside of the site.
No matter what, when you are ready to submit your application you can do it yourself, or you can hand the whole thing to us. An MM-SEAS Navita Navigator walks you through submitting in Navita, the Coast Guard's new submission portal, on a short video call. No computer, or not up for a video call? Our team gets your application submitted to the Coast Guard for you anyway. A Stress-Free MMC is $399. Two MM-SEAS licensing experts check every page, we pay your Coast Guard fees at submission and charge your card so you never touch pay.gov, and we stay on it with the National Maritime Center until your credential is issued.
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Nate Gilman is President and Co-Founder of MM-SEAS. He hawsepiped from the deck to a 3rd Mate Unlimited license with full STCW compliance over more than 15 years at sea, and is a veteran of the NOAA Commissioned Corps. He works directly with the National Maritime Center, USCG-approved training schools, and vessel operators on credentialing policy, and writes on sea service documentation, evaluation standards, and how mariners move up the license ladder.