I'm trying to accrue taxes and then reconcile them when they are due. The taxes owed are in a separate lookup table (year, taxes owed).

For example, assume month 0 is September, so month 4, 16, & 28 is January when taxes are due. Taxes aren't paid (in this line item) until the project is 100% complete. So, in month 4, year 1's taxes are paid somewhere else (another budget).

Month, Calendar, Completion, Taxes
0, S, 0%, $0
...
10, O, 0%, $0
11, N, 100%, year 2's taxes/12
12, D, 100%, year 2's taxes/12
13, J, 100%, year 2's taxes/12
14, F, 100%, year 2's taxes/12
15, M, 100%, year 2's taxes/12
16, A, 100%, year 3's taxes/12 + all year 2's taxes - what's been accrued.
17, M, 100%, year 3's taxes/12
18, J, 100%, year 3's taxes/12
19, J, 100%, year 3's taxes/12
...
24, S, 100%, year 3's taxes/12
25, N, 100%, year 3's taxes/12
26, O, 100%, year 3's taxes/12
27, D, 100%, year 3's taxes/12
28, J, 100%, year 4's taxes/12 + all year 3's taxes - what's been accrued.
29, F, 100%, year 4's taxes/12
...
36, S, 100%, year 4's taxes/12

The part I can't figure out is how to trigger it to reconcile in the correct month. (i realize the reconcile calc is only needed at the beginning.) I know it's not as hard as I'm making it.

Furthermore, I'd really like to make it so I can change the period when taxes are due, i.e. annually, bi-annual, or quarterly.