This is for form 2210 for the year you are filing (e.g. 2018). It should be calculated for what really was the income for up through prior year periods. 

I often cheat just a bit, when I know one income item triggered the increase, such as capital gain. I remove the offending item (capital gain) from the total for the year. I compute 3/12, 5/12 and 8/12 of that remainder and use CTRL + E to enter that amount as "computed". I then use CTRL+E to enter "actual" amounts for income through that period.