Ad Spend Optimizer Calculator

Weighted ROAS is the blended return across all four platforms, and every platform's dollar allocation scales by the exact same proportion when you change Total Monthly Budget — the RATIO between platforms, which is what determines the blended ROAS, depends only on the four ROAS inputs, not on the total amount being split among them. Doubling the budget doubles every platform's dollar allocation and Expected Total Return together, leaving their ratio, and therefore Weighted ROAS, unchanged.

Each platform's budget share is that platform's ROAS divided by the sum of all four ROAS values, so the four shares always add up to 100% of Total Monthly Budget. Raising Facebook ROAS increases Facebook's share of that fixed pie, which necessarily shrinks the share left for the other three platforms — including Google, whose allocation is calculated last as whatever remains after Facebook, Instagram, and TikTok are funded.

No — it assumes each platform's ROAS stays constant regardless of how much of the budget is allocated to it. In practice, ROAS on real ad platforms tends to fall as spend increases, since the cheapest and most responsive audience segments get exhausted first. Treat the allocation as a starting point based on your current trailing ROAS figures, and re-run the calculator as those figures shift with actual spend.

Facebook, Instagram, and TikTok allocations are each rounded independently to the nearest dollar, which can leave the three rounded amounts summing to slightly more or less than the exact proportional split. Google Budget is set to whatever remains of Total Monthly Budget after subtracting the other three, guaranteeing the four allocations always add up to exactly Total Monthly Budget with no leftover or overage from rounding.