Promotion at Big 4s/MBBs/Boutique consulting firms

For MBA grads assuming the role of associates after graduating, curious to know how the promotion cycle works at Big 4s/MBBs/Boutique consulting firms. Do the promotions occur every year or does it entirely depend on the performance? There is a lot of data about the position and the vertical ladder of management consulting with salaries for each however, not much on the time gap between each position.

Do promotions happen every year, once in 2 years or do they solely depend on employee performance and there is no structure as such? Entering b-school this year and charting out my financial plan just to ensure after how long am I breaking even. Also some estimates on signing bonuses and bonuses for subsequent years with/without promotions would be much appreciated.