In A I have entered the current year.

In C I have entered the month of purchase.
In D I have entered the day of purchase (1st - 31st).
In E I have entered the year of purchase.
In F I have entered the amount of the purchase.
In G I have entered the life of the assets.
In I I have entered the salvage value.

In K I have entered the following =SLN(F,I,G)

What I want to do (with a function if possible):

I want K to calculate mid-month SL depreciation.
Let say an assets was purchased on January 16 for $700, with a life of
7 years. A normal year (full year) would calculate $100 worth of
depreciation.

With mid-month depreciation, if an asset is purchased after the 15th of
the month, you start depreciating the first of the next month.

In the example above, the depreciation would be $641.67 (700/12*11).

How do I do this?