How is the waiting period calculated for a woman whose husband has died?

The questioner:
Honorable Shaykh, may Allah grant you success, a woman asks and says: Her husband passed away on the eighth day of the blessed month of Ramadan, before the sun set. When does her waiting period begin? When does it end? And will she be sinful if she adds a day out of caution?

The Shaykh:
She is required to observe a waiting period of one hundred and twenty days, which is four months, or one hundred and thirty days, which is four months and ten days. She counts one hundred and thirty days, and her waiting period ends. So she observes the waiting period by the number of days: one hundred and thirty days, four months and ten days. Yes.

The questioner:
And will she be sinful if she adds a day out of caution?

The Shaykh:
It is not permissible for her to add to the waiting period. It is not permissible to do this, because this is an addition to what is prescribed. It is not a matter of caution. This is a known matter; the days are known and do not require caution. Yes.