TurboTax automatically calculates UCC based on what assets are left in the class, and what CCA amount you are taking, and you can't change it. Double check that you've entered your dispositions correctly if you had anything in that asset class before the adding the DEIP items.

1. I have no assets before start adding DIEP assets
2. All my assets are DIEP
3. Turbotax autofills CCA amount fields (sometimes claiming not the full amount, sometimes after editing assets and changing nothing Turbotax changes CCA as he pleases even if nothing was changed)

What should i see if all my assets are DIEP and it`is my first business year?
If I left  CCA field unchanged after creating expense assets then expenses aren`t fully deducted. What you mean by entering dispositions? As what i can do is either fill CCA to claim for the year as Maximum CCA, or check as no assets left in this class

You can change the CCA amount. 

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