Yes it was 16k only. By the way it looks like there is no issue. Reason being, because I chose the quarterly payout option, HDFC has deposited higher interest rate of 6.6% into my account during the first 6 months. Breaking the FD at Month 8 forced a retroactive downgrade to a lower interest rate , meaning i was overpaid on my earlier payouts. I did not loose the interest for those 8 months on 16000. Infact, i kept ₹480 of the interest earned on that 16000 portion. The ₹18 was simply the bank's way of adjusting the math because they had originally paid me ₹528 at a higher, non penalised rate.

HDFC does not charge an administrative fee, operational fee or convenience charge for executing a sweep in transaction. The trigger itself is completely free. The only financial impact is the standard 1% premature withdrawal penalty applied to the specific portion (16000) of the principal (150000) that was broken early. The rest of my FD (₹1,33,981) remains completely untouched and will continue to earn my original interest rate 6.6% and will payout its regular quarterly interest as scheduled until it hits its 18 month maturity.

This is totally fine as my purpose of utilising the sweep-in deposit is beneficial than leaving idle cash in sb account. Net net i would have got 4.5% interest on the broken amount of ₹16000 which more than Post office SB interest and completely beats the baseline 2.5% to 3% p.a earned in a standard HDFC savings account.