How do you forecast sales units?
Compound base monthly units by the growth rate across the horizon to get the underlying trend, then add a seasonal uplift for the peak months. Separating trend from seasonality keeps a good Christmas from being mistaken for permanent growth.
Sales Forecast Calculator formula
Base trend = Base units x ((1 + g)^n - 1) / g Seasonal uplift = Average monthly units x Uplift% x Peak months
Worked example: 500 units a month growing 3% over 12 months trends to 7,096 units. Two peak months at 40% add 473, giving 7,569 units forecast.
How this works in your browser
Each month compounds the previous month's units by the growth rate, then applies any seasonal multiplier for that month before totalling the horizon. Applying seasonality as a multiplier on top of the trend rather than folding it into the growth rate keeps the two separable, which matters because they behave differently: the trend persists while the seasonal uplift reverses. All figures are in units rather than currency, so the output feeds straight into purchasing decisions. Computed locally.
Who uses Sales Forecast Calculator
Purchasing decisions
Decide how many units to order for the coming period.
Seasonal planning
Order ahead of a peak with a weighted forecast rather than a flat one.
Cash flow planning
Anticipate when stock spend will fall.
Scenario comparison
Run optimistic and pessimistic cases before committing.
Frequently asked questions
How far ahead should I forecast?
At least as far as your total lead time, otherwise you are ordering for a period you have not forecast. Beyond three to six months accuracy falls away quickly for most small businesses, so forecast far enough to order and revisit it monthly.
How do I handle seasonality?
Apply an uplift to the months that genuinely peak, based on what those months did last year relative to your average. Applying a flat growth rate across a seasonal business is the single most expensive forecasting mistake, because it under-orders before the peak and over-orders after it.
What base figure should I use?
A recent actual average rather than your best month. Anchoring on an exceptional month builds optimism into every subsequent projection, and stock bought against it is what ends up in clearance.
How accurate will this be?
It is a projection of the assumptions you entered, not a prediction. Its value is in comparing scenarios and in giving your ordering a defensible basis, so run a pessimistic case alongside the expected one and order somewhere sensible between them.
Are my sales figures uploaded?
No. Everything is calculated in your browser.