The basic formula that you need is
which gives you the number of ways in which items can be taken from a group of items.
Since you hold 13 cards, the total number of possible hands that partner can hold is
Of these the total number of hands not containing either of your two specified cards will be .
The second expression divided by the first gets you the probability that partner holds neither of the two specified cards and that works out to be approximately 0.4386.
Therefore the odds will be roughly 56-44 (slightly better than even money), in your favour.
This assumes of course that you have no information gleaned from any bidding. It's as if you have picked up your hand and are making the opening bid with no other information other that what you see in your own hand.