It was third of Jamadi-al-Thani, year eleven after Hijrah.

Fatimah (AS) asked some water and washed her body and performed ablution with it. Then she wore a new cloth and lied in bed and put her hand under her cheek and said: I will die now.‌ And then she was martyred as a result of hard blows and injuries. At that time, she was only 18 (according to common words) and she had been alive only 95 days after Prophet’s death (according to common words).
She passed away being angry with Abu Bakr and Omar as Sunnis most reliable books and Shias greatest books mention. She did not talk to them at the ending of her life and naturally Abu Bakr regret about attacking Fatimah (AS) home when he was dying was useless.

Source: en.shafaqna.com