using my debit mastercard as credit card?

Yes.

To run something “credit” just means a manner of processing a transaction. If your card has a Mastercard or Visa logo on it, a transaction can be processed using that card number as “credit.”

Similarly, you can run your card as “debit” anywhere that shows a symbol that matches one of the ones on the back of your card, like Cirrus. Most gas stations and grocery stores accept debit transactions from many different systems, each of which has a different symbol.

You said you have sufficient funds in your account.

Something to be aware of is this – if you purchase debit, the transaction generally goes through quicker, like if you went to the ATM, and will show up pending on your bank account pretty much immediately (depending on financial institution).

However, with “credit” transactions, especially with online transactions and gas stations, you may show a $ 1.00 pending item, and then you may also see your charge (or sometimes you just see the $ 1). Many merchants have their system set up to run a $ 1 charge just to see if your card is valid, and the transaction will either change to the amount of your purchase when it posts, or it will drop off.

Also, “credit” transactions usually end up posting a few days after you run ‘em, because the merchant actually has to submit a receipt for the purchase (whereas with debit, they don’t because you ran your PIN). So, until they show actually “posted,” factor them into your balance like you would an outstanding check.

EDIT: To respond to one of the above comments – you DO have protections – actually, more “protection” as it’s your deposited money coming out rather than just coming out of a credit account. It’s called Regulation E.

If you see anything unauthorized, you should shut down your card immediately. Just like with credit, you may need to wait until the item posts before you can dispute it, but your bank has a specific timeframe in which to resolve your claim and cannot refuse to investigate your claim.

Yes, it’s probably better to use a credit card on the Internet, simply because on the off-chance something happens, they’re stealing your credit instead of your actual money, but you are still protected by law.

Protect yourself by making sure you’re going through a legitimate web site and using a secure computer (no malware, secure connection, etc.). Use common sense.