What is a saturation curve?
A saturation curve is a chart or model showing how results, such as conversions or revenue, grow as you increase ad spend, and how that growth levels off. It shows the point where extra spend adds very little.
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How to read a saturation curve
Spend is on the horizontal axis and results are on the vertical axis. A concave curve starts steep and then flattens; an S-shaped response can start shallow, steepen, and flatten later. The appropriate shape depends on the channel, data, and model.
The steepness at your current spend tells you what the next dollar is likely to return.
Using the curve for budget decisions
Each channel has its own curve. Comparing them helps you see where an added dollar would do the most good and where a channel is close to its limit.
Marketing mix models estimate saturation curves from historical spend. Spend-scaling tests can check them, since a curve is only as reliable as the range of spend it was fitted on.
Common questions
What is the difference between a saturation curve and diminishing returns?
Diminishing returns is the idea that each extra dollar brings less. A saturation curve is the model or chart that shows how this happens for a channel.
What does the flat part of the curve mean?
It means extra spend adds little. That money may be better used on another channel, or the channel may need new audiences or creative.
How do you build a saturation curve?
You fit a curve to historical spend and results, usually within a marketing mix model. It works best when your spend has varied enough to show how results respond.
Can a curve change over time?
Yes. New creative, audiences, competition, or seasons can shift it, so refresh your estimates regularly.
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