Sea-time calculator
CHIEF. TOOLS · Free
Add the sign-on and sign-off dates of your contracts and see your sea service in STCW months, in days and in 30-day months. For planning your next certificate of competency.
How the calculator counts
Enter each contract from your discharge book or sea service testimonial. Both the sign-on and the sign-off day count. Contracts that overlap, such as a handover on the same ship, are counted once.
STCW regulation I/1 defines a month as a calendar month, or 30 days made up of periods of less than one month. So the calculator takes the whole calendar months of each contract, from a date to the day before the same date of the next month, and adds up the days left over from all contracts at 30 days to the month. That is the first and largest figure.
Some administrations count days instead. The USCG and AMSA convert days at 30 days to the month, and the USCG counts 360 days to the year. The calculator shows those figures too.
The last figure is the one the CHIEF. app shows in your profile and CV: days on board divided by 30.4375, the average length of a month, rounded to the nearest whole month. For a certificate application, use the STCW figure or your administration’s own count.
Rules differ by administration
| Administration | What counts as a day | Months, years and limits |
|---|---|---|
| STCW | A day on board, as your discharge book or testimonial shows it. | A month is a calendar month, or 30 days made up of shorter periods. |
| USCG (United States) | Eight hours of watch or day work. On vessels under 100 GRT the OCMI may accept less, never under four hours. A 12-hour day counts as one and a half days only on vessels authorised to work a two-watch system. | 30 days to the month and 360 days to the year. Only time on board counts, not time employed. |
| AMSA (Australia) | Eight hours of work in 24 hours. More hours on the same day do not make a second day. | 30 days to the month. |
Your administration decides. Check its current rules before you apply, and send it the dates from your documents, not this summary.
What the calculator does not do
- It counts calendar days, not hours: it cannot apply the eight-hour rule, the 1.5-day credit for 12-hour days or credit for short days.
- It does not split sea service, standby, yard and leave time or apply their limits. Enter only the days that count as sea service.
- It does not check the vessel type, tonnage, propulsion power or rank your certificate asks for.
- It is an estimate for planning, not an assessment. Only your administration’s assessment counts.