The Piggy Bank grows by one Golden Egg every time something gets upgraded or purchased. You can 'crack' it for the aforementioned price, which will reset the counter to 0 and give you all the Golden Eggs inside the Piggy Bank. To crack open the Piggy Bank you need to purchase this in-game with the price of $2.99 or £2.99. Each time it is cracked it gains a bonus, starting at 0% on the first crack and gaining a +10% each crack from then on from each level. with level 1 currently giving a 2% more. It can also gaining bonus by completing contract. Piggy bank it’s often much more worted purchasing it because exponential golden egg growth could make difficult the right moment to crack it, here below are some tips.
In order to fill it up quickly, you should prestige often. Make sure to not skip housing or vehicular upgrades; get them all. If you're really extreme, don't skip eggs after late-game prestiges. When to crack it is your choice, but there are two main options.
If you want to spend money to maximise efficiency per buys, 15-25 thousand is a good rule of thumb, followed by 35-50 thousand on the 2nd crack.
If you want to maximise efficiency per money, crack it a lot later (around 200,000).