Underpayment penalty and estimated taxes

[FinallyInSeattle]

I understand the rule of paying either 100% of last year's taxes or 90% of current year's taxes to avoid a penalty. 

Do I avoid a penalty if I reach 90% of what I owe in the last estimated tax payment of the year or is there a penalty for not paying enough earlier in the year?

[PattiF · Accepted solution]

Yes, there is a penalty for not paying enough throughout the year, The IRS has been enforcing this more in the last few years.

Here is some information from the iRS: