How do we pay estimated taxes for income made only part of the year?

[KathrynElizabeth7]

My husband recently started making independent contractor income that does not have tax withheld at the very end of May. He's only gotten 3 independent contractor paychecks so far this year and at this time we really don't have a solid idea as to what his income for the next 6 months will be.

How do we figure out what we need to pay in estimated tax payments for the 7.5 months of independent contractor income so we don't incur penalties?

[Bsch4477]

He will be taxed along with his other earned income (after deducting the standard or itemized deduction) at whatever his tax bracket is and in addition will owe about 15.3 percent self employment tax on his net self employment income.  Withholding is due the 15th of April, June, September and the following January.  This year the April and June estimated tax is due by July 15. 

[Critter-3]

Rule of thumb ... send in 20% of your gross income for now as estimated payments if your total income is going to be less than $60K for the year ... later when you know what your profit margin will be like you can adjust it.