If I remember correctly, in the last century the party in control of the presidency has lost an average of 26 seats in the house in each mid-term election. The average senate loss is about 3-4 seats. Your numbers are pretty much repeating history.
But, do note that the first midterm election tends to be nicer for the presidential party. Those historical numbers are closer to 17 house seats and 1 senate seat lost. It depends a lot on redistricting, number of retiring congressmen, etc. Real Clear Politics is estimating +7 GOP senators and +16 house (but there are many tossups there).
I'm going to go out on a limb and estimate 15 house losses and 5 senate losses, but there is still a lot of time between now and November. So, I reserve the right to change my mind.