Inland sea days count for 100-Ton NC renewal. If short on days, you have four options, including open-book tests and renewal courses.
No. The renewal process only looks for the number of sea days on navigable waters. The days all count the same wherever they occur, (i.e. Inland, Great Lakes, Near Coastal, etc.)

If you are going to have less than 360 days in the previous five years of your renewal application date there are FOUR different options to renew your Captain's License. 46 CFR § 10.227 lays them out and we will go through each way for you. https://www.law.cornell.edu/cfr/text/46/10.227
The most likely options are 1 and 2. Options 3 and 4 apply to instructors.
Option 1) Open Book Take Home Test
You can take an open book take home test for all National Endorsements you hold. This will be emailed to you after your application is approved at the National Maritime Center for all domestic licenses that you hold.
As an example, if you currently possess a Master 200 GRT Near Coastal, an Able Seafarer Special and Lifeboatman, you will take an open book test for each of them. Remember, you have been sailing and got your original domestic license so the open book test should be a breeze!
The NMC will charge you one Examination fee of $45 no matter how many National Endorsements you are renewing.
Option 2) Take a Renewal Course
You can also take a USCG approved renewal course for each of your National endorsements.
There are actually four total pathways. You can explore all four in this guide: What do I need to renew my USCG Captain's License with less than 360 days?
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.
MM-SEAS Expert Access is $99 a year. It is your personal guidance counselor for USCG licensing: what training you need next, which sea time counts, and how to reach the credential you want, by phone, email, chat or a 1 on 1 video call. Expert Access members also get $50 off a Stress-Free MMC.
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.