I'm trying to understand if it's possible to convert "part" of the following years into months and, perhaps, days. Specifically, those after the decimal point. Can you help me?

If 0.3 is applied to the beginning of the year, the result is 3 months, 19 days, 12 hours.

If 0.16 is applied, the result is 1 month, 27 days, 9 hours, 36 minutes.

The above figures are based on a 365-day year.

Wouldn’t .25 be 3 months? 3 months is a quarter of the year. (365 X .25 = 91 days) I use this example for simplicity regarding the concept.

I would think of it as a fraction and then convert to a decimal or vice versa.

What I am not clear on is if 4670.16 is how many times 365 fits into 4670? Or, if 4670 is the year 4670? Like on the Jewish calendar? .16 would equal day 58 on a 365 day calendar year (365 x .16) but a Jewish calendar does not have 365 days every year. Or, am I way off in my thinking?

* To take leap-years into consideration, be sure to use 365.25 as your days-per-year – not 365.

1/10th of a year is 36.5 days. So .3 of a year is 109.5 days. or 15 weeks, 4.5 days.

!/10th of a leap year is 36.6 days. So .3 of that is 109.8 days or 15 weeks, 4 days, 19 hours and 12 minutes.

It’s only possible by defining several things, including exactly when on what calendar you mean, and what you mean by a year, exactly, and also what you mean by the decimal notation you are using. Otherwise, Brian and JLeslie above will misunderstand each other.

And, if you’re converting into months and days a decimal notation that’s more like Brian’s than JLeslie’s, then you need to know when the time interval you’re talking about is, and also which calendar you’re using.

It seems to me that (the?) one main context where people would refer to years in decimals and also possibly be interested in converting them to months and days (to get actual dates), would be astronomy. In that context, years tend to mean the time it takes the planet (or possibly some other planet) to complete an orbit about the sun that the planet orbits. And that is measured in an actual scalar amount of time, and may be used in motion calculations, so it’s one of the few cases where it’s actually useful to speak of time in decimal years. That year is NOT 365 days (and sometimes 366 days, as on a calendar) for the Earth – it’s 365 days, 5 hours, 48 minutes and 46 seconds. So you’d work in decimal years, and then when you wanted an actual calendar date, you’d pick the calendar, the actual starting or end point, and calculate the time difference on the calendar in terms of difference in time from one end of the period to the other. You’d calculate in terms of days / minutes / seconds, and let the calendar tell you what day of the month it is, since months are quite irregular and specific to the calendar.

Can https://www.timeanddate.com/ help? They have lots of ways of computing calendar information and related questions.