Free tool
Saturation curve estimator
Are you on the flat part of the curve? Drop in your last 7 days of spend + conversions — we'll tell you the headroom.
Want this running 24/7 on your account?
Free tool
Are you on the flat part of the curve? Drop in your last 7 days of spend + conversions — we'll tell you the headroom.
Want this running 24/7 on your account?
It answers one question: does your cost per acquisition get worse when you spend more? You paste one line per day in the form spend,conversions — at least four days, ideally seven — and it compares the cheap days against the expensive ones.
This is a spend-versus-efficiency comparison, not a time series. The tool ignores what order the days happened in, which is what lets seven scattered days of budget experiments produce a usable answer.
Your days are sorted by spend ascending and split into a low half and a high half. Each half gets a pooled CPA — total spend in the group divided by total conversions in the group, which weights busy days properly instead of averaging daily CPAs. The CPA lift is the percentage increase from the low-half CPA to the high-half CPA.
The lift decides the verdict. Saturating is a lift of 50% or more — your expensive days cost half again as much per conversion. Linear scaling is 15% to 50%, a real but tolerable premium for volume. Scaling efficiently is under 15%, meaning high-spend days are essentially as cheap as low-spend days. Not enough variance appears when your high and low halves spent the same amount, or when the low half produced no conversions at all.
The suggested daily cap follows from the verdict: 120% of the average low-spend day when saturating, 125% of the average high-spend day when linear, and 150% of it when scaling efficiently.
A saturating result is a signal to stop adding budget to this campaign and to add it somewhere else instead — the budget reallocator will show which campaign has the appetite. Linear scaling means push in steps of roughly 20–25% and re-measure after each step rather than doubling and hoping. Scaling efficiently means you have not found the ceiling yet; keep going until the lift crosses 15%.
Two caveats worth holding. A CPA rise can come from creative fatigue rather than saturation — if the expensive days were also the later days, check the fatigue forecast before blaming budget. And a CPA that is technically rising can still be profitable: compare it against your break-even in the ROAS calculator before you cap anything.
Last updated August 31, 2026. All 17 calculators and AI helpers are listed on the free tools hub.
FAQ
It is the shape of the relationship between daily spend and results. Early on the curve is close to a straight line — double the budget, roughly double the conversions. Past a point the curve flattens: each extra dollar reaches people who are less likely to convert, so cost per acquisition rises. The saturation point is where that flattening starts, and it is the ceiling on how far a campaign can scale before efficiency pays for the volume.
The estimator needs at least four days of data and genuine spread between your cheap and expensive days. If every day sat at roughly the same budget there is no curve to fit and the tool returns 'not enough variance' rather than inventing a shape. Swing daily spend by about 50% either side of your average across a week and re-run.
No, it is a starting point derived from where you already have evidence. If you are saturating it suggests 120% of your average low-spend day, deliberately pulling you back toward the efficient part of the curve. If you are scaling efficiently it suggests 150% of your average high-spend day — a step beyond anything you have tested, so treat it as the next experiment rather than a proven number.