Is there a calculator for quarterly estimated tax?

Its not simple. You have to pay estimated taxes on the profits of your company since you no longer have someone taking withholding out of your salary. So you have to estimate what the profits of your company will be (that is what you receive minus your business expenses). Some of the expenses are just deducted as they occur; meals and lodging are more complicated, since you would have had to eat even if you didn't have a business. You can go to irs.gov and download publications on this subject. Finally, your taxes will depend on what your final profit is. You report that on your 1040 along with all your other income and losses. The estimated tax will be on your adjusted gross income on the 1040.