The form used to determine estimated taxes is the 1040-ES. This form is available at Internal Revenue Service offices and on the IRS website.
Those who earn income that is not subject to withholding tax should use the 1040-ES to estimate how much tax they need to pay. Self-employed people, those who collect rent, alimony or dividends should all refer to the 1040-ES.
Estimated tax must be paid if a taxpayer will owe at least $1,000 in 2015, although farmers, fishermen or higher-income taxpayers are subject to different rules.
To figure estimated taxes, a taxpayer will need the Estimated Tax Worksheet, the Tax Rate Schedules and the 2014 tax return.