If you are self-employed and anticipate owing income tax to the Canada Revenue Agency, you must submit quarterly income tax payments. The CRA should send you a reminder so you know how much to pay. You can pay the amount shown in box 2 of your reminder. However, that amount is based on your income tax owed over the last two years; it does not reflect your current earnings.
To ensure you are paying enough tax and to avoid a large bill at tax time, you may want to calculate your business tax liability every quarter. Take your revenue and expenses into account, and then remit the income tax you owe based on your quarterly profits.