That's a miss statement of the safe harbor provisions. There are 3 basic safe harbors but the relevant ones here that allow you to avoid underpayment penalties are paying the lesser of
a)90% of the tax for the current year, or
b)100% of the tax shown on the return for the prior year. (If last year's return shows AGI over $150K (for married filing jointly) then change that "100%" figure to "110%.)
