Use the following equation to determine how much experience is required to get any weapon capped at its current level:

n = Increase your weapon will grow after every level obtained. For example, to get from level 1 to 2, you need 1,000 experience. From level 2 to 3, you need 1,125 EXP. n = 1,125 minus 1,000, which in this case is 125. So n for this weapon would equal 125.

x = The total number of levels you will need to cap (Star) your weapon. For example, from 1 to 21 (Star) for Tier 1 weapons requires 20 levels (21-1=20).

b = The base experience your weapon contains. For example, Axis Blade at level 1 requires 1,000 experience to reach level 2. 1,000 is the base experience.

(xn-n)(x/2)+bx = Total experience necessary to cap a weapon. An easier way to understand this equation is x times n minus n. Then, multiply that value by x divided by 2. Then, add b times x.