Harpy Glossary

CTC (Contribution to Change)

Amazon & D2C glossary · Harpy Media

CTC (Contribution to Change) measures how much a single factor — one SKU, one channel, one cost line — moved a larger total between two periods, usually expressed in percentage points or basis points. If portfolio profit fell 4%, CTC answers: which products caused it, and by how much?

What is CTC?

It’s the accountability layer of performance analysis. Totals tell you something changed; CTC tells you WHO changed it — converting a vague quarterly review (“profits dipped”) into a precise list (SKU 14 cost you 3.1 points; SKU 3 gained you 1.2). Allocations without it are arguments; with it, they’re arithmetic.

Why portfolio math needs it

A catalog of 40 SKUs moving in different directions produces a net number that hides every story inside it. CTC decomposes: group-by-group contribution to the period’s delta, so the 5% growth masking a collapsing product line becomes visible before the collapse completes. The method: compute each unit’s profit change (this period minus last), divide by last period’s total — the percentage-point blame/credit each item owns. Sort descending. The top of that list is where management attention actually belongs, regardless of what the mood of the meeting says.

Using CTC for decisions, not just post-mortems

Three applications: resource reallocation (the negative-CTC cluster gets the diagnosis; the positive cluster gets the budget), goal setting (“replace SKU 14’s 3-point drag with 3 points of growth from the launch pipeline” — targets that name their sources), and exit discipline (a SKU that appears in the top negative contributors for three consecutive periods has made its case for retirement). CTC turns variance from a thing that happens to you into a list of decisions you own.

CTC for factor X = (X’s profit this period − X’s profit last period) ÷ total profit last periodIn points or basis points; sort by size; assign named owners to the top five.

In practice

A brand’s quarterly profit dips 3.4% despite record revenue. CTC decomposes: one packaging-cost error on the top SKU (S2,315 negative), one ad-campaign overspend (S1,180), offset by a bundle that’s quietly compounding (+S2,050). Three line items explain 97% of the delta — each gets an owner and a fix, and the next quarter’s review starts with last quarter’s five named items, still tracked. Variance becomes a ledger instead of a feeling.

⚠️ Watch out. A monthly review stares at aggregate numbers and debates interpretations for an hour. Nobody decomposes; nobody owns; the same three drivers appear next month and the month after, entering every meeting as fresh news. Unexplained variance doesn’t resolve itself — it just gets tenure.

💡 Harpy tip. After any period where profit moved more than 2%, run a five-minute CTC: top three negative contributors, top three positive, named owners. Meetings become shorter immediately.

How Harpy Media helps

Period variance gets decomposed, named, and owned in our reviews — a dip is a list of five SKUs, not a mystery.

CTC FAQ

What is Contribution to Change?

A measure of how much one factor (SKU, cost line, channel) moved a total between periods — the attribution math for performance variance.

How is it expressed?

Usually in percentage points or basis points of the total metric’s change — sum the factors and you reconstruct the delta.

Why does it matter for Amazon sellers?

It converts vague portfolio movements into named, ownable drivers — which is the difference between reviewing numbers and acting on them.

Want these numbers watched for you, every week?

Book Free Consultation