Formula results not adding correctly?

It looks like it is calculating correctly, based on the formulas you give it.

The first tool I used in looking at this is the evaluate formula tool. If you are unfamiliar with this tool: https://support.office.com/en-us/art...la_one_step_at

F12 appears to simply add the number of days in E12 to the date in D12. If you add 70 days to the end of August, you should get a date in early November.

D12 seems to be calculating the earliest data between this entry and the next instance of "task category 1" in C (row 90) and the result is correctly 29 August.

E12 seems to be calculating the number of days between the latest date in column F of the same range (6 November in F80) and the date returned in D12. There are about 70 days between 6 November and 29 August, so this seems correct.

I didn't go farther than that, but so far, the calculations seem correct.

If you continue using the formula evaluate tool as you drill down through the calculations, can you find the cell that seems to be causing the error?

Another useful debugging tool that does not get much air time: R1C1 notation. One of the "difficulties" of working in A1 notation is that, when relative references are used, copies of the formula "look" different. In R1C1 notation, copies of formulas always read exactly the same. F214 and F224, indeed have the exact same formula. However, these are relatively simple addition functions based on D214 and E214 and D224 and E224. Looking at these cells, the formulas in D214 and D224 are different, and E214 and E224 are different. The lookup/MATCH() parts of these formulas in row 214 start their lookups 2 rows below row 214 (row 216). However, in the row 224 formulas, the lookups begin in the same row (row 224). If you run through the formula evaluator, this causes these lookups to return row "1", which is the same row as the lookup function, which causes the INDEX() part of the function to return the entire remaining column, rather than the small subset.

I also notice that, because the search string is "sub task", even changing the formula to the same as the 214 formula may still be in error. Copying the formula from 214 to 224 causes the lookup to find the "next" instance of "sub task" which is below the "task category" entry in row 252. So the MAX and MIN functions start looking beyond the current "task category" into the next "task category". I am guess that the lookup should stop searching at the "task category" row. If this is correct, in addition to correcting the formula, you might add a "dummy" sub task row above each "task category", so that the formulas in D and E will not search beyond the next task category.