In planning your payments for 2013, you may not want to pay any more than is necessary to avoid a penalty. You can avoid a penalty for 2013 by planning payments in 2013 that meet the 90% current-year test or the 100%/110% prior-year safe harbor.
If you expect your income, deductions, and tax credits for 2013 to be about the same as they were for 2012, and you will not have any additional liabilities for 2013 that you did not have for 2012, such as for alternative minimum tax (AMT), self-employment tax, household employee taxes, penalty taxes, or recapture taxes, you can base your 2013 withholdings and quarterly estimated tax installments on 90% of your 2012 total tax.
If you expect your 2013 total tax to be lower than your 2012 total tax, such as where your income has dropped, you can base your 2013 withholdings and estimated tax installments on 90% of the estimated 2013 total tax.
You can use the 2013 Estimated Tax Worksheet in the instructions to Form 1040-ES for 2013 to figure the required annual payment under the 90% test, as well as under the prior-year safe harbor test discussed next.