Breakeven Point

aU = bU + FC + P

or

aU - bU = FC + P

Where:
a = selling price
b = variable costs
U = "per unit"
FC = fixed costs
P = desired profit

The breakeven point is the amount of sales at which a company no longer loses money. It is the point at which the amount of money gained from sales equal the amount of money lost by revenue.
This calculator does not calculate the amount of sales needed to reach the breakeven point, however. It calculates the amount of sales needed to reach the desired profit. This is a valid use of the term, though: for many companies, reaching the breakeven point isn't an option (because they want to make money) so they refer to the point of reaching their desired profit as their breakeven point.
However, if you wish to calculate the true breakeven point, simply put "0" in the box labeled "Desired Profit."

This calculator will give you the amount of units you need to sell in order to reach your breakeven point (it solves for the variable U.) If you want to know the amount of money you need to make (aU) instead of the number of units you need to sell, simply multiply the answer this calculator gives you by the selling price of each unit (a.)

Works Cited
Siegel, Joel G., Jae K. Shim, and Stephen W. Hartman. Business Formulas. New
     York: McGraw-Hill, 1998.