My 2015 AGI is going to be about 2.5x my 2014 AGI, some of that is going to be 1099 income, so I am trying to figure out my estimated quarterly tax payments. In filling out the 2015 estimated tax worksheet, I see that line 14c (required annual payment to avoid a penalty) is the smaller of my tax liability for 2015 * 90% or my required annual payment based on prior year's tax (line 63 on my 2014 1040). Because my income this year is so much different than my income last year, lines 14a and 14b are very different, but when I follow the worksheet and take the lower of the two numbers (my 2014 tax liability) and subtract my expected income tax withheld for 2015, it is a negative number, suggesting that I do not need to make estimated tax payments.

My question is, should I just start making estimated tax payments based on my expected 2015 tax liability (and will I be penalized if I do not do so?) or can I just wait until the end of the year because my total anticipated income tax withholding from 2015 is more than my total tax liability in 2014?