Insight · MeasurementMOFU
CAC, ROAS, MER or contribution margin: which KPI should you run on?
The short answer
The best marketing KPI is the one that matches how your business makes money. A D2C brand with thin margins, a B2B services firm with long sales cycles and a subscription app should not run on the same number. Pick one main KPI, a handful of supporting metrics, and make sure everyone reads them the same way.
The main options
| Metric | What it tells you | Best used for |
|---|---|---|
| ROAS | Revenue per rupee of ad spend, as the platform reports it | Optimising campaigns within a channel |
| MER | Total revenue ÷ total marketing spend | Checking overall efficiency without double-counting |
| CAC (new-customer) | Cost to acquire one new customer | Growth decisions and budget planning |
| Contribution margin after marketing | Profit left after variable costs and marketing | Whether growth is profitable |
| LTV : CAC | Value of a customer relative to their acquisition cost | Businesses with repeat purchases or subscriptions |
| Payback period | How long until a customer repays their CAC | Cash-constrained businesses |
| Cost per qualified lead / per sale | What a good lead and a sale really cost | Lead generation |
Which one for your business
- eCommerce and D2C — run on contribution margin after marketing or MER, with new-customer CAC as the growth guard-rail; use platform ROAS only inside channels
- Lead generation (services, real estate, education, B2B) — run on cost per qualified lead and cost per sale, fed back from the CRM
- Subscriptions and repeat-purchase brands — run on new-customer CAC against LTV, with payback period
- Apps — run on cost per activated or paying user, not cost per install
- Marketplaces — run on TACoS and contribution margin per order, not ACoS alone
Why ROAS shouldn't be the main KPI
Platform ROAS is useful for comparing campaigns within Meta or within Google. As a company scorecard, it misleads: each platform claims every conversion it touched, so totals overlap, and returning customers flatter the numbers. Read why your ROAS lies for the detail. Use ROAS to optimise, and MER or margin to decide.
Set the target from your economics
A KPI only helps with a target that comes from your numbers:
- Break-even ROAS from your margin — use the break-even ROAS calculator
- Maximum CAC from customer value — use the CAC:LTV calculator
- Maximum cost per qualified lead from your close rate and deal value: if 1 in 10 qualified leads closes and a sale is worth ₹50,000 in gross margin, a qualified lead can cost up to about ₹5,000 before you lose money (illustrative)
Supporting metrics
- Spend and revenue (or leads) by channel, weekly
- New versus returning customer revenue
- Conversion rate and average order value
- Lead-to-qualified and qualified-to-sale rates for lead businesses
- Creative health: hook rate and frequency on the main campaigns
Mistakes to avoid
- Running the business on platform ROAS
- Mixing new and returning customers in CAC
- Cost per lead as the main KPI for lead generation
- Targets set from competitors' numbers rather than your own margins
- Changing the KPI every month
The same month, read four ways (illustrative)
A D2C brand spends ₹10 lakh in a month and records ₹40 lakh in revenue. Meta and Google together claim ₹52 lakh. Returning customers account for ₹15 lakh. Contribution margin after product, shipping, payment fees and returns is 45% of revenue.
| Lens | Calculation | Reading |
|---|---|---|
| Platform ROAS | ₹52 lakh ÷ ₹10 lakh | 5.2x — overstated by double-counting |
| MER | ₹40 lakh ÷ ₹10 lakh | 4.0x — real overall efficiency |
| New-customer revenue per rupee | ₹25 lakh ÷ ₹10 lakh | 2.5x — what acquisition is buying |
| Contribution after marketing | ₹40 lakh × 45% − ₹10 lakh | ₹8 lakh profit before fixed costs |
Each number answers a different question. Only the last tells you whether the month made money.
Leading and lagging indicators
Main KPIs like contribution margin and new-customer CAC are lagging: they tell you what happened. Leading indicators — creative hook rate, cost per add-to-cart, lead-to-qualified rate, landing page conversion rate — move first and tell you what's likely to happen. Track both: leading indicators for weekly decisions, lagging ones to judge strategy.
Changing your KPI as you grow
Early-stage brands often run on cost per first purchase or cost per qualified lead while they find product-market fit. As repeat data builds, LTV:CAC and payback become possible. At scale, contribution margin after marketing and incrementality tests become the real tests. Changing KPI as the business matures is healthy; changing it every month is not.
Frequently asked questions
Is MER better than ROAS?
For business decisions, usually yes, because it can't be double-counted. ROAS remains useful for optimising campaigns inside one platform.
What is a good CAC?
One that your customer value and margins can afford. Compare CAC with LTV and payback period rather than with industry averages.
Should agencies be judged on ROAS?
Better on business outcomes — MER, new-customer CAC, cost per qualified lead or contribution margin — agreed up front and read from your own data.
How often should we review KPIs?
Weekly for trends, monthly for decisions, quarterly for the KPI and targets themselves.
What if different teams want different KPIs?
Agree one main KPI for marketing's contribution to the business, and let teams use supporting metrics for their own optimisation. Our marketing analytics team builds this scorecard.
What's the difference between CAC and CPA?
CPA is the cost of any tracked action — a lead, a sign-up, a purchase. CAC is the cost of a new customer, usually calculated from total marketing spend and new customers.
Should we include agency fees in CAC?
For business decisions, yes — fully loaded CAC includes fees, tools and creative. Media-only CAC is useful for comparing channels.
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