If you're a citizen or resident of the United States whether you must file a federal income tax return for the year depends on your filing status and gross income for the year. Gross income means your income from all sources whether in the form of money, goods, property, or services. However, you don't needs to count Social Security income unless your total income including Social Security exceeds certain levels. Nor need you include tax exempt income such as tax exempt retirement income. However, you do include all the profit you earned from selling your main home, even if all or part of it is exempt from tax.
All adult individuals who are not claimed as dependents by someone else must file a return if their gross income for the year exceeds specified levels. These amounts are adjusted each year for inflation. For example, if you're single, you had to file a return for 2015 if your gross income was at least $10,300; $11,850 if you were 65 or older. If you were married filing jointly, you had to file a return if your gross income was at least $20,600; $21,850 if one spouse was 65 or older, $23,100 if both spouses were 65 or older. Check the IRS website for current annual filing thresholds.
A child or other dependent must file an income tax return (2016) if his or her:
unearned income for the year was more than $1,050
earned income was more than $6,300, or
gross income (earned and unearned income) was more than the larger of $1,050 or earned income (up to $6,300) plus $350.
"Unearned income" means income earned from investments, such as interest or dividends. Earned income means income earned from working.
If a child’s only income is interest and dividends, and the child was under age 19 at the end of the year or was a full-time student under age 24 at the end of the year, and certain other conditions are met, a parent can elect to include the child’s income on the parent’s return. If this election is made, the child does not have to file a return.
Generally, a child is responsible for filing his or her own tax return and for paying any tax on the return. But if a dependent child who must file an income tax return cannot file it for any reason, such as age, then a parent, guardian, or other legally responsible person must file it for the child. If the child cannot sign the return, the parent or guardian must sign the child’s name followed by the words “By (your signature), parent for minor child.”
The IRS really wants self-employed people to file tax returns, so the rules are stricter for them. If you're self-employed, you must file a return if your net earnings from self-employment are $400 or more.