Read the 1040 instructions, and follow them. This works if you don't have a complicated situation, such as business income or if you need to calculate penaltie

Read the 1040 instructions, and follow them. This works if you don't have a complicated situation, such as business income or if you need to calculate penalties for shortfalls on quarterly filings. Have a CPA do your taxes periodically, then use last year's taxes as a guide for the current year. Typically what I do is write a small program that asks the questions in the 1040 form, then gives me a print out of what goes in each field. For my case, I have one source of income (employer), a couple times I've sold stock, and I have a mortgage, am single, but support my SO and her 4-year old grandkid. I've done my own taxes for the last 20 years, and only a couple times took it to a professional (once to H&R block when I sold stocks, and last year to a CPA). Both times the tax forms were exactly what I figured out on my own.