It depends on a lot of factors, like fuselage interference, lift and twist distribution, planform, taper ratio, induced angle of attack etc...
But, basically, what it comes down to is a proportionality to aspect ratio (AR) to correct for a finite wingspan where there are losses at the wingtips. For a rectangular wing, you can use
1-1/AR
For an elliptical wing,
1-0.57/AR
So, for an aspect ratio of 6, you'd get a value between 0.83 and 0.90