Know what your marketing actually caused.
Stella runs controlled holdout tests that separate the revenue your ads caused from sales you’d have made anyway, so you know your true incremental ROAS.
Included in every plan, free and up. No credit card.
Trusted by growth teams who left enterprise measurement vendors
Every platform says it drove the sale.
Credit isn’t cause. A holdout shows what your ads actually caused by comparing markets where they ran with comparable markets where they didn’t.
The test is won in the design.
Control markets have to track your test markets closely before the experiment starts, and promos and price changes belong in the design, not the footnotes. If the markets didn’t track before the test, no model rescues it afterwards.
Models compete. Best fit wins.
Stella tests several models against how your markets behaved before the test, and picks the best fit before anyone looks at the result.
Illustrative. Best-fitting candidate on the pre-period criteria, chosen blind to the result.
Know what happened here.
See the estimated impact under the spend, timing, and conditions you tested.
How Rylee + Cru measured a 6.57 incremental ROAS on brand shopping →
Now turn the result into a curve.
Your holdout gives the model a causal anchor, so Stella can estimate returns beyond the spend level you tested.
Illustrative.
With Stella, you know.
What a channel actually caused.
The revenue that only happened because the ads ran.
Whether they would have bought anyway.
The conversions your platforms are double-counting.
Your incremental ROAS.
Not the platform number. The one that reconciles.
Whether branded search is incremental.
The test most brands avoid running.
What happens if you turn it off.
Before you find out the expensive way.
Whether the result is solid enough to act on.
The estimate, its uncertainty range, and its significance. Not a lone point estimate.
Ask Stella about holdouts.
Where to run one, how much spend it takes to detect lift, or what a study you already ran really showed.
Hear it from the brands we run measurement for.
Incrementality questions, answered.
What is incrementality testing?
Incrementality testing measures the sales your marketing caused, as opposed to sales you would have made anyway. Stella is an incrementality and marketing measurement platform: it runs controlled geo holdouts, turning ads off in some markets and comparing them with closely matched markets where ads kept running, to measure incremental revenue, incremental ROAS, and causal lift.
How is incrementality testing different from attribution?
Attribution assigns credit for a conversion to the touchpoints a customer passed through. It cannot tell you whether that customer would have bought without the ad. Incrementality testing answers exactly that, by comparing markets with and without the ads. Credit tells you where people came from; a holdout tells you what the spend caused.
How does Stella pick test and control locations?
Location selection is where most holdouts are won or lost. Stella analyzes your pre-period history and selects control markets that have moved together with your test markets, so the comparison is valid before the test even starts. It works even for dense, multi-location footprints, using a weighted synthetic control.
How does Stella choose which model to trust?
Several candidate models compete on pre-period fit, how closely each one tracked the test market before anything changed. The best-fitting candidate on those criteria is selected before the treatment effect is looked at, so nobody can shop for the result they wanted. You see the pre-period R² and MAPE alongside the estimate and its interval.
How long does a holdout take?
A geo holdout typically runs 20 to 28 days, longer for high ad-stock channels. If you want a usable read sooner, Always-On Incrementality (Professional and up) produces daily directional iROAS while the holdout incubates the rigorous number.
How do incrementality tests and media mix modeling work together?
They answer different questions. A holdout measures what a channel caused at the spend level you tested. A media mix model estimates how returns change as spend moves. Instead of treating them as competing answers, Stella uses your holdout results to calibrate the model, so its response curves are grounded in causal evidence.
What can I do on the free tier?
Run a real holdout study, no credit card. Free includes one holdout and one media mix model a year, on data you upload. Already ran a holdout elsewhere? Drop it in and see what our location selection would have recommended before you upgrade anything.
What plan includes incrementality testing?
Every plan, free and up. Always-On Incrementality, which keeps the number current between tests, starts at Professional ($3,000/mo).
Know what your marketing actually caused.
Run a real holdout on your own numbers, free. Or have a founder design the first one with you.