High-Low Method Calculator: Split a Mixed Cost into Fixed and Variable Parts
Use the high-low method to split a mixed cost into variable cost per unit and fixed cost, build the cost equation, forecast costs and compare with regression.
How it works
Variable cost per unit (b) = (cost at highest activity − cost at lowest activity) ÷ (highest activity − lowest activity) · Fixed cost (a) = cost at highest activity − b × highest activity (= cost at lowest activity − b × lowest activity) · Total cost Y = a + b × X · Activity for a budget = (budget − a) ÷ b
Many costs are mixed: part of them is fixed each period (a base fee, a supervisor’s salary, equipment lease) and part rises with activity (power per machine hour, fuel per mile). The high-low method splits a mixed cost using just two observations, the periods with the highest and the lowest activity. The change in cost between them divided by the change in activity is the variable cost per unit; subtracting that variable cost from either total leaves the fixed cost. The result is a cost equation, Y = a + bX, that you can use for budgets and forecasts. Paste your data, one period per line, and the calculator picks the highest and lowest activity periods for you. That is the step students most often get wrong: the points are chosen by activity, not by the highest or lowest cost. You can also enter the two points directly. With three or more periods the calculator also fits a least-squares regression line using every period, shows R² and lists how far each period sits from the high-low line, so you can see whether the two extreme periods are representative. Forecasts within the range of your data (interpolation) are more trustworthy than those outside it (extrapolation). The method assumes cost behaves linearly within the relevant range and that the two extreme periods are normal. It is quick and easy to explain but ignores every other data point, so regression is usually more accurate. Adjust older costs for inflation before using them.
Worked example
Maintenance cost over six months ranges from $26,000 in June (1,800 machine hours, the lowest activity) to $38,750 in April (3,500 hours, the highest). Variable cost per hour = ($38,750 − $26,000) ÷ (3,500 − 1,800) = $12,750 ÷ 1,700 = $7.50. Fixed cost = $38,750 − $7.50 × 3,500 = $12,500 per month, so Y = $12,500 + $7.50 × X. At 3,000 hours the estimated cost is $12,500 + $22,500 = $35,000, of which 35.7% is fixed. A least-squares line through all six months gives about $7.43 per hour and $12,830 fixed (R² 0.9984), a forecast of $35,113 at 3,000 hours, so here the two extreme months are representative.
Sources: Accounting Simplified: High-low method (factory overhead and inflation-adjusted payroll examples) · Pearson Channels: High-low method calculator (electric bill and coffee shop examples) · Omni Calculator: High-low method
Frequently asked questions
How do you calculate variable cost with the high-low method?
Take the periods with the highest and lowest activity, subtract the lower total cost from the higher one, and divide by the difference in activity. For example, ($30,000 − $25,000) ÷ (6,000 − 4,000 units) = $2.50 per unit. Then fixed cost = $30,000 − $2.50 × 6,000 = $15,000.
Do you choose the high and low points by cost or by activity?
By activity. Use the periods with the highest and lowest activity level (units, hours, miles), even if another period had a higher or lower cost. Choosing by cost is a common mistake that gives the wrong variable rate.
What are the limitations of the high-low method?
It uses only two data points, so an unusual high or low period distorts the result. It assumes costs are linear, ignores inflation unless you adjust the data, and is unreliable outside the observed range. Least-squares regression uses all the data and is usually more accurate.
What is the difference between the high-low method and regression?
The high-low method draws a line through the two extreme activity points. Least-squares regression finds the line that best fits every point, and its R² tells you how well a straight line explains the cost. This calculator shows both so you can compare.
How do I use the cost equation for a budget?
Plug the planned activity into Y = a + bX. With $15,000 fixed and $2.50 per unit, 7,000 units cost $15,000 + $17,500 = $32,500. To find how much activity a budget covers, use X = (budget − a) ÷ b.
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This calculator is for educational purposes. Double-check important results before acting on them.