[elena_elphie]

Whether you are filing as a pro is completely irrelevant, you will have to pay penalties if both:

a) you pay less than 90% of your total tax liability for the year through withholding or quarterly payments.

and

b) you pay less than 100% of your tax liability for last year through withholding or quarterly payments.

Actually its slightly more complicated than that, but that's the general idea, filing as a professional or not has nothing to do with it.