What I found as a decent rule-of-thumb is that you take their after-unlocked figure (so their L1->2 amount) and multiply by 120. It gets pretty easy once you've done it a few times... Take Gingerbread (since that's the one I happen to be looking at and the math is easy). 1.2M after unlocking. +20% = 1.44M. Add a few zeros, and 144M to L10