ddb and fractional periods

Hi, I'm trying to make use of the ddb worksheet function for calculating depreciation. It seems straightforward for whole periods, however, when I use fractional periods I don't understand how MS Excel derives its values.

For Example,

The format of the function is DDB(cost,salvage,life,period,factor)

The underlying calculation is,

period 1: cost * (factor/life)
accum. depreciation (accp1) = deprec. for period 1
period 2: (cost - accp1) * (factor/life)
accum. depreciation (accp2) = accp1 + deprec. for period 2
period 3: (cost - accp2) * (factor/life)
.........
and so on.

However, the above formula changes when dealing with fractional periods and I don't understand how.

Does anyone have an idea how MS Excel calculates the DDB using fractional periods?

Thanks, Steve

Please Login or Register  to view this content.