I got a letter from IRS that my tax penalty is under calculated. I used the TurboTax software. Can someone from TurboTax help reconcile this?

[Bsch4477]

The TurboTax penalty is an approximation since the program can’t know exactly when the tax will be paid which is a factor in assessing interest. 

[VolvoGirl]

The penalty on 1040 line 38 is  just an estimate so it is possible for the IRS to recalculate it and send you a refund or a bill for more.  Very common.  In fact you can even select to leave it blank and let the IRS figure it for you.  

You can go though form 2210 and see if you come up with less.  Go to Federal Taxes tab or Personal tab, under Other Tax Situations and select Start by the Underpayment Penalties.