Growth Engineering Playbook · Wave 5
Your best channel is the worst place for your next euro.
Budget gets split evenly or poured into whatever has the best average ROAS — both ignore diminishing returns. A channel with a great average return can be fully saturated, so its next euro barely moves. The correct rule is marginal: keep shifting budget to the channel with the highest marginal return until they all match — water-filling against one shadow price. This grades the current Northstar Outfitters plan against that optimum, and finds the profit-maximising budget where the marginal euro stops paying for itself. Deterministic, client-side.
Loading channel curves…
Current vs optimal spend
Grey is the current plan; blue is the optimal allocation at this budget. The delta is where the money should move.
Diminishing returns
One channel's net-contribution curve, with current & optimal marked.
Reallocation plan
Marginal ROAS is the return on the next euro. At the optimum, every funded channel's marginal ROAS matches — that's the signal you've allocated correctly.