Well, the Hijri date 18 Jumada Al Oula 1420 corresponds to the Gregorian date Sunday, 29 August 1999. This date lies in the fifth month of the Hijri year 1420 AH, which is Jumada Al-Awwal of 1420 AH. Both this Hijri and Gregorian date occur on the single day that is Sunday without any doubt. The Arabic date 1420/05/18 is calculated using the Umm Al-Qura calendar and the sighting of the moon. One thing to remember is that this Arabic date may occur on different Gregorian date depending upon the region and country and obviously the moon.
If you are still not sure about the date then you can use our Arabic date converter.
The following is the conversion of the Gregorian date 29 August 1999 to its equivalent Arabic date.
The following is the conversion of the Arabic date 18 Jumada Al Oula 1420 AH to its equivalent Gregorian date.
أَلَمْ يَعْلَمُوٓا۟ أَنَّ ٱللَّهَ يَعْلَمُ سِرَّهُمْ وَنَجْوَىٰهُمْ وَأَنَّ ٱللَّهَ عَلَّٰمُ ٱلْغُيُوبِ
Know they not that Allah knoweth both their secret and the thought that they confide, and that Allah is the Knower of Things Hidden?
Surah At-Tawba(9:78)