There are various strategies that can be used by someone with a job to avoid paying estimated taxes with respect to income not subject to withholding. Some strategies include:
However, be sure that the strategies you use address not only the income tax on your contract work but also any self-employment tax that may be owed.
The tax on the investment income in excess of $1,700 (may change after 2007) of a child under age 18, based on the parents’ marginal tax rate and computed on Form 8615.