For 2015, my monthly withholding total for all of 2015 on my 1099-R will be about $3800 but my tax due will be about $4200. The estimated difference between tax withheld and tax owed will be about $400. My understanding is there is no penalty charged as long has the difference between withheld and owed is less than $1000.
FWIW, last year (2014) my withholding was about $6000 due to higher income so this year I won't qualify for the Safe Harbor of Withholding 100% of last year.
Am I correct in thinking that there will be no penalty as long as the difference between tax due and amount withheld is under $1000?