A form that an individual files with the
IRS to calculate and pay taxes based what he/she believes his/her ultimate
tax liability will be. In other words, one uses Form 1040-ES to estimate taxes and pay them, usually on a
quarterly basis. One must file Form 1040-ES if one has
income that is not subject to
withholding. If the estimation is wrong, the filer may receive a
refund (or pay more to the
IRS) when he/she files the actual
tax return.