PPR relief

While calculating the period of exemption and the chargeable period under the PPR relief question,doing it in the excel sheet and even on the exam excel sheet, the number of days in between the period can be calculated easily by subtracting the two dates,while it never matches with the answer of Kaplan book and Revision kit ,since it calculates in month(maybe the days being inconsistent according to months). Can the difference be calculated in excel itself and days be used in calculating the relief,instead of breaking fingers and counting months ?

I didn’t knew where to post these sorts of questions,and please Tax Tutor reply me fast since I am sitting exam on coming Tuesdays.