If a contractor sends an invoice for services rendered in the previous tax year and I pay it in the current tax year does the amount go on the old tax year or the new tax year.

On the new tax year regardless of your accounting method,i.e., cash or accrual method. Tax deductions offer a way to indirectly reduce the amount of taxes you owe. When you claim a tax deduction, your taxable income is reduced by the amount of the deduction.so, You deduct the service expense when you pay for it. In other words, if you pay your serviceexpenses early, you can claim the deduction early, and if you pay your service expenses late, you have to claim the deduction late, as well, but you don't lose the deduction.