T90D (Trailing 90 Days)
T90D (Trailing 90 Days) is the rolling quarter: the most recent ninety days of performance data, updating daily. It is the window long enough to contain a full sales cycle and short enough to still describe the present.
What is T90D?
T90D (Trailing 90 Days) is the rolling quarter: the most recent ninety days of performance data, updating daily. It is the window long enough to contain a full sales cycle and short enough to still describe the present.
It is where strategic judgements live. A week or a month responds to what changed recently; ninety days shows whether the change was structural. Average sales velocity, advertising efficiency across a complete cycle, and the shape of demand all read more truthfully over a quarter than over any shorter period.
What the quarter captures
Three things shorter windows miss. A complete promotional cycle, so a sales spike from a single event does not masquerade as a trend. Enough data points for average velocity to be stable, which matters because inventory and replenishment planning depend on it. And the natural rhythm of a category — whether demand is genuinely growing or simply oscillating within the same range.
That stability is the point. Decisions taken on ninety days are less likely to be reversed next month, which means less churn in pricing, inventory, and campaign structure. Where a brand keeps changing course, the cause is usually a decision-making window that is too short for the effect being measured.
Using it for strategy
Three applications. Inventory planning, where average velocity over a quarter sets the replenishment base and reduces both stockouts and overstock. Advertising strategy, where efficiency measured across a full cycle is the fair basis for budget allocation. And long-horizon metrics such as ranking trajectory, which only become visible over months anyway.
Read with the trailing year it provides context, and read with the trailing month it shows direction. The combination answers the question that matters: the business at a stable baseline, and the current movement within it.
In practice
A brand sets replenishment quantities from ninety-day average velocity rather than from the most recent month, and allocates advertising budget on efficiency measured across the same window. Ordering becomes steadier, both shortages and overstock fall, and fewer decisions need reversing the following month.
How Harpy Media helps
Planning discipline is part of our operations work: replenishment and budgets set from stable quarter-length averages, with shorter windows used to steer rather than to reset the plan.
T90D FAQ
What is T90D?
Trailing 90 Days — a rolling quarter of performance data used for mid-term analysis, including average sales velocity, advertising efficiency, and replenishment planning.
Why not plan from monthly data?
Because a single promotion or seasonal shift can distort a month. A quarter contains a full sales cycle, so averages are stable enough to plan against.
What is it best used for?
Inventory planning, advertising budget allocation, and ranking trajectory — decisions that need to hold for months rather than weeks.
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