Islamic law is easy and does not require complex calculations or science

The Prophet ﷺ said, "We are an illiterate nation; we neither write, nor know accounts. The month is like this and this, i.e. sometimes of twenty nine days and sometimes of thirty."  

عَنِ النَّبِيِّ ﷺ أَنَّهُ قَالَ: «إِنَّا أُمَّةٌ أُمِّيَّةٌ لاَ نَكْتُبُ وَلاَ نَحْسُبُ۔ الشَّهْرُ هَكَذَا وَهَكَذَا - يَعْنِي مَرَّةً تِسْعَةً وَعِشْرِينَ وَمَرَّةً ثَلاَثِينَ۔»