There are two ways to calculate the cut-off for the middle-class. One is strictly based on income meanwhile the other is based on relative cost (otherwise meaning regional price differences) focusing primarily on being smart with your money.
In Canada, going by the measure of income, the middle-class ranges from 25% to 40% of the population, depending on your leeway that is +/- 25% of median income or +/- 33% of median income. The other definition of middle-class relies your expenses to income, meaning how much of your income is left after your maintenance expenses. The definition says someone is middle class if they have 30% of their income left after paying bills. In Canada, where the average personal debt is 160% to income, that means NO MIDDLE-CLASS even while everyone seems to be working (article).