Recall from our discussion of variable costing that  revenue - variable costs = contribution margin, and that this works for totals (total revenue - total variable costs = total contribution margin) as well as per unit calculations. The derivation of the breakeven point below uses the following notation: SP = sales price/unit TR = total revenues [ = quantity sold * sales price] TC = total costs TVC = total variable costs [ = quantity produced * variable cost per unit] VC = variable cost/unit TFC = total fixed costs NI = net income X = number of units CM = contribution margin per unit TCM = total contribution margin CMR = contribution margin ratio For simplicity, we'll assume that production equals sales; we won't worry about finished goods inventory Now we can derive the relationship for the breakeven point. TR - TC = NI but TR = SP(X), so we can substitute as follows: SP(X) - TC = NI but  TC = TFC + TVC, and TVC = VC(X), so we can substitute as follows: SP(X) - VC(X) - TFC = NI. Factoring out the common term, we get X[SP - VC] -TFC = NI, but SP - VC = CM, so we have CM(X) - TFC = NI, but at breakeven, NI = 0, so we can transpose and get CM(X) = TFC. To solve for X, divide both sides by CM: X = TFC/CM; recall that CM is contribution margin per unit. Therefore, the breakeven point in units = TFC/[CM/unit], and the breakeven in dollar sales = TFC/CMR, where CMR = CM/SP The foregoing analysis assumes that there is only one product, or that all products have equal contribution margins. When there is more than one product, the contributions have to be weighted in proportion to each items relative sales volume. Suppose we produce 2 products: A and B. Product A constitutes 25% of our sales volume and Product B is 75%. The weighted average contribution margin would take these proportions into account as follows: Weighted average CM = [CM (A) * .25] + [CM (B) * .75] When we find the breakeven point, the answer we get will be a composite of one fourth product A and three fourths product B. To find the actual units of A and B, the breakeven in units has to be multiplied by the proportions in which the respective items are sold. If you are ready to go on to the CVP Applications, click next >>>