This is a tool for estimating California income tax. It is intended to help you determine how much California state income tax you would owe given the data you provide. The California income tax is based on the results of the federal tax computation, so the value for many of the fields can be found on the federal return.
The California income tax calculation starts with the federal adjusted gross income (AGI). Then, for each difference between the federal and California tax law an adjustment is either added or subtracted from the federal AGI. On the California tax return form 540, these adjustments are aggregated into Subtractions on line 14 and Additions on line 16.
In the input fields in this tool, fields that need to be subtracted or added to the federal AGI are listed in the corresponding section "Subtractions from Federal AGI" or "Additions to Federal AGI". However, in the actual calculation on a California tax return, these fields may not end up where you would expect. Some of the fields that seem like additions may actually be subtracted from the subtractions rather that added to the additions. And the reverse may be true as well. This tool will calculate the "Additions" and "Subtractions" values in the section "Estimated Tax Calculation" so that these values will match the values calculated on a California tax return.
The formula for calculating the California income tax is also provided to show, at a high level, how the tax is calculated. The value of each item in the tax formula is shown in the "Estimated Tax Calculation" section.
The remainder of this document describes the fields that are computed (blue) and the fields where you can enter data (green). The fields are listed in the same order as they appear in the tool. This is also the same information that is displayed in the tool tips.