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.
Based on an IRS table, an amount that reduces a business deduction taken for payments on an auto leased for a minimum of 30 days.