Allocating by marginal return, not equal or historic splits
The instinct in most planning rooms is to split a budget evenly, or to take last year’s plan and nudge it. Both approaches quietly assume that every channel responds to spend in the same way - and that assumption is almost never true. The disciplined alternative is to allocate by marginal ROAS: the return earned by the next pound of spend, not the blended average a channel happened to post last quarter. A channel can show a strong average while its next pound returns almost nothing, because the cheap, responsive audiences have already been bought.
The rule that follows is simple to state and powerful in practice. Keep moving budget toward the channel with the highest marginal return until every channel returns roughly the same marginal value. At that point no further reshuffle improves the total, and the budget is working as hard as it can. This marginal mindset is the backbone of serious media planning, and it is exactly why even a well-funded plan can be improved without spending a penny more.
How saturation caps each channel - a worked example
Every channel obeys a saturation curve: returns flatten as spend rises and the most responsive audiences are exhausted. That curve effectively caps how much budget a channel can absorb profitably, and it is the reason marginal return falls even when average return still looks healthy. Allocation that ignores saturation keeps pouring money into yesterday’s winner long after its ceiling has been reached.
Take a £50,000 monthly budget with a retargeting line that is heavily saturated - its next pound of spend returns a marginal ROAS of just 1.3x - sitting alongside an under-funded Search line whose next pound still returns 4.0x. Moving £10,000 from retargeting to Search costs nothing extra, yet every reallocated pound jumps from 1.3x to roughly 4.0x of incremental return until Search begins to saturate in turn. Blended return rises with no increase in total budget, purely because the spend now sits where the curve is still steep. Reallocating from saturated to under-funded channels in this way is the single highest-leverage move in most plans, and it is invisible to anyone reading averages alone.
Funnel-stage splits and why allocation matters for media planning
Allocation is not only a channel question - it is a funnel-stage question. Spend split across upper-funnel demand creation, mid-funnel consideration and lower-funnel harvesting behaves like a portfolio: over-fund harvesting and you simply collect demand that already exists; starve the upper funnel and the harvesting channels slowly weaken as their pipeline dries up. The same marginal logic applies across stages as it does across channels, so the right split balances the marginal return of creating new demand against the marginal return of converting it.
This is why allocation sits at the centre of forecasting rather than reporting. Decided well, it determines how much return a fixed budget can possibly earn before a single ad runs; decided by habit, it leaves money on the table every cycle. Testing those trade-offs in advance is the job of scenario planning, which lets you compare allocations side by side - and it is what makes media planning without spreadsheets a meaningful upgrade rather than a cosmetic one.
How ElenIQ allocates budget
ElenIQ forecasts each channel’s saturation curve from historic data, then allocates by marginal return so the next pound always lands where it earns the most. Because the analysis runs before spend is committed, you can reallocate from saturated to under-funded channels - and re-balance funnel stages - on a forecast rather than discovering the ceiling the expensive way in-market. The result is an allocation that is deliberately uneven, because the optimal plan rarely looks tidy.
Rather than defending an equal split or last year’s plan, you can test allocations directly with the budget allocation simulator, then assemble the full plan in the media plan builder. Both keep the focus on the same question: where does the next pound work hardest, and what is the most total return this budget can buy?
Related terms
- marginal ROAS - the return earned by the next pound of spend, which should drive every allocation decision.
- saturation curve - how returns flatten as spend rises, capping how much budget a channel can absorb.
- media planning - the wider discipline of deciding where and when advertising budget is deployed.
- scenario planning - comparing allocations side by side before any spend is committed.
Frequently asked questions
What is budget allocation?
Budget allocation is the division of a fixed advertising budget across channels, campaigns and funnel stages to maximise total return. The strongest plans allocate by the marginal return of each option - the value of the next pound spent - rather than by habit, equal splits, or simply repeating last year’s plan.
How should you allocate a marketing budget across channels?
Allocate to the channels where the next pound of spend earns the most, then keep moving budget until every channel returns roughly the same marginal value. Equal or historic splits ignore the fact that each channel saturates at a different rate, so the right allocation usually looks uneven and shifts as spend grows.
Why is equal or historic budget splitting a problem?
Equal splits and copy-paste-from-last-year plans assume every channel responds the same way, but channels saturate at very different points. A channel that was the star performer last year may already be at its ceiling, while an under-funded channel still has cheap headroom. Allocating by marginal return captures that difference; fixed splits leave return on the table.
How do saturation curves affect budget allocation?
Every channel follows a saturation curve - returns flatten as spend rises and audiences are exhausted. That curve effectively caps how much budget a channel can absorb profitably. Good allocation reads each channel’s curve and stops feeding it once its marginal return drops below another channel’s, redirecting the spend to where it still works hard.
How does ElenIQ approach budget allocation?
ElenIQ forecasts each channel’s saturation curve from historic data, then allocates by marginal return so the next pound always lands where it earns the most. Because the analysis runs before spend is committed, you can compare scenarios and reallocate from saturated to under-funded channels without learning the hard way in-market.