How a dasha end date is calculated
A dasha end date is the start date plus the length of the period in years, using the year of 365.25 days.
What it is
For a period of N years starting on a given date, the end is the start plus N times 365.25 days. The tool computes each end and the start of the next period from the same arithmetic.
How it is worked out or read
Partial first periods, given by the balance at birth, use the remaining fraction of the lord's years, so the first end date is not a whole number of years.
Where it appears on this site
The end dates are in the dasha tool. See leap years and dasha years.
Start, length and end
Every dasha period has a start, a length in years and an end. The end is the start plus the length, and the next period begins at exactly that moment. The tool uses a year of 365.25 days, so a period of N years lasts N times 365.25 days, and the end date follows by adding that number of days to the start. Because the arithmetic is continuous, the end of one period and the start of the next are the same instant, and no gap or overlap is produced.
The first period is the exception, since it starts at birth but only its balance remains. Its end date is therefore the birth date plus the balance, which may be a fraction of a year. Every later period begins at a full length, and its end is found in the same way from its start.
Worked example with dates
Suppose a Venus mahadasha begins on 1 January 2010. Venus's period is twenty years, which is 7305 days. Adding 7305 days to 1 January 2010 gives a date in the first days of January 2030, allowing for leap days in the interval. The Sun's mahadasha then starts that same day and lasts six years, or 2191.5 days. The tool performs these additions to the nearest day and shows the dates. A reader can check any end date by adding the days to the start.
Because leap years fall in the interval, the number of days in twenty years is not the same as twenty times 365. Using the year of 365.25 days spreads the leap days evenly, which keeps the dates close to the calendar over long periods.
Checking results and rounding
When a reader checks an end date by hand, small differences of a day can appear from rounding, from the convention used for the start time and from the time zone of the birth. These differences are normal and do not change the sequence of periods. A reader who needs an exact date for an important purpose should confirm the birth time and the calculation method and, if the timing matters, compare with a second source.
Doing the calculation step by step
Take the start date, write it as a day count from a fixed reference, add the number of days in the period, and convert the result back to a calendar date. Doing this on paper once or twice makes the logic of the timeline clear. The steps are the same for every period, so a reader who has understood one has understood them all. Writing the reference date and the running total in a table helps avoid slips when a period is long or when several are added in sequence.
When the result is checked against the tool, the reader should expect agreement to within a day. Any larger difference points to a different start date, a different year length or a different treatment of the first partial period. Finding the source of the difference is usually more useful than adjusting the answer.