That depends on the AMOUNT of income AND the TYPE of income.
Filing is not required if all your income is from W2 Wages, Interest, Dividends and Other Miscellaneous Income (excluding Social Security) AND if this total income is less than the Standard Deduction plus personal exemptions.
A Single person's standard deduction is $5,700. Add a personal exemption of $3,650. Total $9,350. That means on the first $9,350 of income there is no Income Tax liability and NO filing requirement. If the taxpayer is 65 or older, or blind add another $1,400 to the standard deduction for a total of $10,750.
But it's not really that simple. Let's assume this single person's only source of income was $1,000 of self employment income. The Income Tax is zero BUT the return must be filed due to Self Employment Tax liability on Self Employment Income of $400 or greater!
Suppose the person's self employment income is $200 and that's all. Sounds like no filing requirement. The self employment income bottom line may be only $200, but let's say the business of the self employed person generated $1,000,000 in sales with enough expenses to generate only a $200 profit.
YES, there is a filing requirement! Think about it.. a million dollars passing through a self employed person's hand should be accounted for.