What are the charges for currency conversion in TD Ameritrade. Is the currency conversion fee lower or greater than interactive brokers.?

TD Ameritrade uses a preferential rate with DBS, which is not published on their website and you will have to enquire with their CSOs to find out the rate for the day. From my conversations with them, they update the rate at 2pm on working days.

I have found the rate to be relatively close to the spot rate that IBKR offers, much better than most other brokers. However, they do not convert your currency immediately and may take 1-2 working days. This means that the rate is not locked in and your currency may get converted at a different rate than the one you were quoted at deposit.

If you are converting very large amounts of currency, IBKR may be better as they offer the live spot rate and extremely low commissions for currency exchange. They also give you the certainty of what rate your currency will be converted at. For smaller amounts, TD Ameritrade will do just fine.