Days calculation ?

Calculation of interest on capital A/c

Suppose, amount taken as on 1-3-2012 from directors.

As per above example days calculation is 1-3-2012 to 31-3-2012 = TOTAL 31 DAYS

But in Tally. ERP 9 days calculation is 1-3-2012 to 31-3-2012 = TOTAL 30 DAYS

IN TALLY.ERP 9 date of 31-3-2012 has not taken i.e. The calculation is 1-3-2012 to 30-3-2012= TOTAL 30 DAYS

WHY 31-3-2012 THIS DATE IS  NOT TAKEN IN CALCULATION & WHAT IS RESONS OF THIS?????

Regards,

SEEMA