Sea Time Calculator
Enter your sign-on and sign-off dates for each voyage and get your total sea service in days and 30-day months — the running tally toward a certificate or revalidation.
Sea time is the currency of a ticket
Every step up the certificate ladder is paid for in sea time. Cadets need qualifying service before they can sit for their first certificate of competency, and officers need it to revalidate. Keeping an accurate running tally of sign-on and sign-off dates means you know the moment you have enough — and you can back it up with your discharge book when the administration asks.
Standing the watches that build that time? Lay out the rotation with the Watch Schedule Planner.
Frequently Asked Questions
How is sea time counted?
Sea service is counted inclusively — both the day you sign on and the day you sign off count as sea days — so joining and leaving on the same date is one day. This calculator sums the inclusive days across every voyage you enter and gives you a running total in days and in 30-day months.
Why is a month treated as 30 days?
Because STCW and most maritime administrations count sea-service in months of 30 days for certificate purposes, rather than calendar months of differing length. So 90 days is exactly three months and 105 days is three months and fifteen days. The tool shows the whole months plus the spare days so you can see how close you are to the next month.
Does all my time on board count as qualifying sea service?
Not necessarily. Administrations set rules about what counts — the ship must usually be seagoing and above a certain size or power, the service must be in a relevant capacity, and some require a proportion of actual watchkeeping. Time in port, on leave, or standby may be treated differently. This is a personal running tally; your flag state or licensing authority makes the final ruling on what qualifies.
What do I need to prove my sea time?
Keep your discharge book, sign-on and sign-off records, and letters or testimonials of sea service from the master or company. Those are the documents an administration checks against, and keeping your own tally with this tool makes it easy to see when you have enough qualifying service to apply for a certificate or revalidation.
A personal running tally for planning — not an official record of qualifying service. Your maritime administration decides what service counts toward a certificate.