Ad Spend Allocator

Marginal ROAS is the return on the next incremental dollar of spend, not the average across all spend. It matters because platforms have saturation curves: at low spend, ROAS is high; as spend climbs, the algorithm reaches deeper into the audience and each new dollar earns less. Allocating by marginal ROAS shifts budget toward platforms still climbing — and away from platforms that look healthy at average but are wasting their incremental dollars.

Three signals: (1) frequency — if your average user has seen ads 5+ times in 7 days, you're high saturation. (2) Trend — if ROAS has dropped 15%+ as you've scaled spend over the last 30 days, you're medium-to-high. (3) Audience reach — if you're reaching 60%+ of your defined audience monthly, you're high. New campaigns, new audiences, or recent creative refreshes typically reset toward low saturation.

Real saturation curves require historical spend-vs-revenue data fit with non-linear regression — most teams don't have it tidy. This tool gives you 80% of the right answer with 20% of the inputs. For the rigorous version, run incrementality tests (Meta Conversion Lift, geo holdouts) quarterly, or use a media-mix modeling tool (Northbeam, Measured) if you're at $1M+ monthly spend.

10-20% of any platform's budget per week, maximum. Algorithmic platforms (Advantage+, Performance Max, Smart Performance) re-enter exploration when budget changes dramatically — the first 5-7 days after a major shift is noise, not signal. Move in increments and let each shift bed in for 7-10 days before re-evaluating.

Yes, but treat it differently from social platforms. Google Search captures existing demand — it doesn't create it. If your demand pool is fixed, scaling Search past your demand ceiling won't help. Mark Search as 'high saturation' once branded search and high-intent non-brand keywords are fully covered; further scale needs Meta/TikTok TOF to create the demand Search captures.

Two likely causes. First, the algorithm needs 7-10 days to re-converge after a 15%+ budget swing — first-week ROAS is noise. Second, the platforms you scaled may have lower saturation than you estimated; check frequency and audience reach. If after 2-3 weeks the projected lift hasn't materialized, walk the shift back to 50% and let the data settle before deciding.