Demand Trend Checker

Seasonality is the part of product research people nod at and then ignore, right up until they order 5,000 units of a Christmas item in September and eat storage fees until March. This calculator shows how much a Q4-heavy product actually spikes, using just two numbers you already have.

Enter what share of your annual sales fall in Q4 (spread over October, November, December) and your current average monthly sales. The tool backs out an annual run rate, splits the Q4 slice across three months, and shows how much hotter those months run than a normal month.

The math assumes your current month is a typical non-peak month, so don't run this off a December number or it'll tell you Q4 is mild. Use an average month from somewhere boring like March.

Why this matters: a product doing 400 units a month average but 1,600 in Q4 needs inventory staged months early, and it needs cash to survive the quiet months. The Q4 lift number tells you whether you're running a business or running a Halloween costume that sits dead 11 months a year.

Two cautions. First, a single Q4 share hides the shape — Q4 isn't flat; November and December dwarf October. Second, this is a planning lens, not a forecast. One weird year, a new competitor, or a supply hiccup shifts the curve. Use the lift to size inventory and set cash aside, then watch the real numbers each quarter. The sellers who get burned aren't the ones who didn't calculate — they're the ones who calculated once and never looked again.