Outside the Box - I hope you don't mind, I took some of your tax brackets and formulas and combined them with the 1040 workbook from excel1040.com. It does not do a lot of the background calculations (making sure you are eligible for various deductions and credits, AMT, etc.) that the full excel1040 does, but the layout makes the inputs easy to pull from a prior 1040 and make simple adjustments.
Google Sheet LinkFile > Make a copy . . . and then edit your "local" copy in your Google sheets.
I am going to test it against your calculations and see what differences I find.
Yellow Fill with Blue font are inputs; Pink fill is formulas
Known Limitations:
- Head of Household is an option, but I haven't tested it at all
- Married filing Separately is NOT an option
- I haven't setup anything to actually use the Long Term Capital Gains Rate
- I haven't touched the AMT calculations
- There are other fields filled in gray that I haven't setup yet
- Child Tax Credit for 2018 not phased out for high incomes (new limit is $400,000 for Married Filing Jointly, so won't affect majority of people)