If he had not paid estimates during year..........

and had no withholding from an employer to offset the tax..........

Then he would likely pay underestimated tax PENALTIES for the calendar year 2016......no interest involved.

The requirement for estimated tax payments during the year is avoided if taxpayer qualifies (1) as farmer (or fisherman)...........(2) and files (3) AND pays by March 01.

If taxpayer misses March 01.......and FILES   AND   PAYS by April 15, then the cost is just the underestimated tax PENALTY plus the regular tax.  No interest involved.

The underestimated tax penalty is computed---- for farmers--- on form 2210F..........and amounts to ABOUT 6% per year........but because of the way it is calculated, it is typically less than that.

The tax laws are very precise and very clear in this area.

2210F can be obtained on the net.

By the way........and often asked question is---------- If I have no money, is it better to NOT file?

Answer------- ALWAYS file, even if do not have the funds to pay the taxes.

Reasons....

..... when tax returns are not filed.....and taxes not paid...........the cost is 5% of the tax per month.....up to 25%.........and then after the late filing penalty stops at 25%, a late payment penalty kicks in at the rate of 1/2 % per month (.005)..........PLUS interest at about 4% on top of all this.......all calculated until payment is made.

........ when tax returns are filed, ........and taxes not paid........ the cost is just the late PAYMENT penalty (.005 per month), plus the interest.

The late filing penalty can be a killer.

And.........this concept applies to most federally required forms that involve tax payments-------- payroll, etc etc.

This is why we file extensions at March 15 (s corps and partnerships), April 15 (individuals and C corps)..........even for sometimes returns that have been filed...........just to make sure that the return avoids the late FILING penalty in the case of a snafu.

Currently there is no penalty for filing an un-needed extension.......but the penalty for NOT filing when needed can be just unreal.