How To Calculate Seasonal Variation |best| May 2026

And every year, she recalculated the indices using the latest three years of data, because seasons shift. A new boardwalk hotel opened, boosting spring sales. Her Spring Index crept up from 0.99 to 1.10.

Leo grabbed a clean napkin and a pen. "You need to calculate seasonal variation. It’s how you separate the 'normal rhythm' of your business from the 'random noise' of life. It takes four steps. Let's use your sales data." how to calculate seasonal variation

"That’s my overall average per season," she said. And every year, she recalculated the indices using

"Now divide that total by 4 to get the 'average season' for next year," Leo said. Leo grabbed a clean napkin and a pen

"Finally," Leo said, "multiply that 'average season' by each Seasonal Index."

"Exactly. That's the 'flat line'—what you'd sell per season if there were no seasons at all." "Now for the magic," Leo said. "For each season, divide its average by the overall average. That gives you the Seasonal Index ."

"I know," Elena sighed. "But the seasons aren't the same every year. Last June was cold, but the June before that was a heatwave. How can I predict anything?"