Marine Daylight Passage Window Calculator
Compare passage hours with your explicitly dated sunrise and sunset instants.
A QUICK WALKTHROUGH
How to use this tool
- Enter dated sunrise, dated sunset, explicit offsets and passage hours.
- Calculate the result.
- Copy the report or download it as TXT.
Formula and units
Daylight hours = (sunset UTC − sunrise UTC) ÷ 3600000. Margin = daylight − passage. If passage fits, latest departure = sunset UTC − passage hours. Otherwise no feasible daylight departure is shown.
Scope
Provide real calendar dates in years 0001–9999 and explicit Z or ±HH:mm offsets. Sunset must be later in UTC and may be on another date. Passage may be zero. There is no automatic sunrise data or inferred browser timezone. Output timestamps have millisecond precision. Arithmetic only, not safe-navigation advice.
Local processing
Your entries stay in your browser. Copy and TXT export include the inputs, formula and scope.
GOOD TO KNOW
Common questions
How should I use the result?
Use it as an arithmetic estimate based on your supplied inputs.