Sheet Metal Design

About 2-3°. There is no real formula; it is merely empirical. Just bend a sample and measure how much it springs back.

GOOGLE Bending Springback Calculator

After a bending operation, residual stresses will cause the sheet metal to spring back slightly. Due to this elastic recovery, it is necessary to over-bend the sheet a precise amount to acheive the desired bend radius and bend angle. The final bend radius and bend angle can be approximated from the sheet thickness, K-factor, material yield strength and modulus of elasticity, and the initial bend angle and bend radius. The final bend radius will be greater than initially formed and the final bend angle will be smaller. The springback factor, Ks, will show the ratio of the final bend angle to the initial bend angle.

Is there any particular formula to calculate this?

Yes, but:

(1) An empirical equation has been developed that predicts springback for a variety of die geometries on the basis of yield strength, thickness, and bend radius; and for some die conditions for bend angle, hold-down, plan view curvature, and punch-to-die clearance. Since an internally consistent rationalization of the predictive equation has also been developed, the predictive equation would appear to have some general validity. However, the extent of this validity cannot be established until it has been more thoroughly evaluated.

(2)

By using variation analysis of the predictive equation for springback, important insights have been established about the interrelationships between variation in springback; variation in yield strength; variation in thickness divided by the nominal thickness, (R/t); and nominal yield strength. This analysis indicates the importance of interactions between the causative variables on variations in springback.

Then is better if you use the Bending backspring calculator