how to calculate 13th day after death

Absolutely, I can help with that. Calculating the 13th day after death is actually quite straightforward. You simply count the day of the death as 'day one', and then count onwards from there. So, the 13th day would be exactly 12 days after the date of death.

If death occurred on October 3rd and you consider this as the first day, then the 13th day will fall on October 15th, just add 12 days to the date of death.

The significance of the 13th day after death can vary from culture to culture. Generally, it's a part of religious or traditional rituals. In many Indian traditions, for instance, the 13th day is a major day of mourning and remembrance, and it's considered the time when the soul completes its transition to the afterlife.