Question: how to calculate time difference more than 24 hours in excel?
Answer: In cell B2 type 12:45, and in cell B3 type 15:30.
Type =B2+B3 in cell B4, and then press Enter. ... 
To display the time as more than 24 hours, select cell B4.
On the Home tab, in the Cells group, choose Format, and then choose Format Cells.
In the Format Cells box, choose Custom in the Category list.