When does the iddah (waiting period) end for a wife whose husband passed away on July 6, 2018, and was buried on July 7?

The waiting period (iddah) is calculated by lunar months (Hijri date), not solar months (Gregorian date). The day of death is included in the calculation of the iddah according to the majority of scholars, differing from the Malikis. Therefore, if a death occurred on 22 Shawwal 1439 AH, the iddah would end on 2 Rabi' al-Awwal 1440 AH.