How marketing ROI, CAC and LTV are calculated
Marketing ROI compares the profit a campaign generated against what the campaign cost. The word doing the work is profit — revenue attributable to the campaign has to be reduced to gross profit before you subtract the spend, because revenue you had to pay cost of goods on was never yours to count as a return.
This is where ROAS and ROI part company. ROAS — return on ad spend — divides attributable revenue by cost, so a campaign is 3.6x whatever your margin happens to be. ROI runs the same comparison on profit. On a healthy margin the two tell a similar story; on a thin one, a ROAS that looks excellent can conceal an ROI that is negative.
Two companion figures decide whether the campaign is worth repeating. CAC is the spend divided by the customers it acquired. LTV is the gross profit a customer produces across their whole relationship with you. The ratio between them, and how quickly CAC is paid back, matter more than the ROI of any single campaign.
Worked example
A campaign costing 2,50,000 that produced 9,00,000 in attributable revenue over 90 days from 120 new customers, in a business running a 60% gross margin. Each customer is expected to generate 18,000 of gross profit over their lifetime.
| Input | Value |
|---|
| Campaign cost | 2,50,000 |
| Attributable revenue | 9,00,000 |
| Gross margin | 60% |
| Attributable gross profit | 5,40,000 |
| ROAS | 3.6x |
| ROI | 116% |
| New customers | 120 |
| CAC | 2,083 |
| LTV : CAC | 8.6 : 1 |
| Payback period | 1.4 months |
Now hold everything constant and drop the gross margin to 25%. ROAS is unchanged at 3.6x — it never sees margin — but attributable gross profit falls to 2,25,000 and ROI turns negative at -10%. The campaign that looked like a clear winner on the ad platform's dashboard was quietly losing money.
How to use this calculator
- Enter the full campaign cost — media spend plus creative, agency fees, tooling and internal hours, not just the ad platform invoice.
- Enter only the revenue you can genuinely attribute to the campaign, and note which attribution model produced it.
- Enter your gross margin so the tool works on profit rather than revenue.
- Enter the number of new customers acquired to get CAC, then your LTV estimate to get the ratio.
- Judge the campaign on LTV:CAC and payback period rather than on ROI alone — ROI over a short window systematically understates campaigns that acquire long-lived customers.
Frequently asked questions
What is the difference between ROAS and ROI?
ROAS divides attributable revenue by cost; ROI divides attributable gross profit by cost. ROAS ignores your margin entirely, which is why a campaign can post a strong ROAS and a negative ROI. Use ROAS for comparing creatives and channels, ROI for deciding whether the spend was worth it.
What LTV:CAC ratio should I aim for?
A ratio around 3:1 is a widely cited benchmark for a sustainable model, with under 1:1 meaning you lose money on every customer. A very high ratio is not automatically good — it often signals you are underinvesting in acquisition and leaving growth on the table.
Why is attribution the hard part?
Because customers touch several channels before buying. Last-click credits the final touch and undervalues everything that created the demand; first-click does the reverse. No model is correct — pick one, apply it consistently, and treat cross-channel comparisons as directional rather than precise.
Should LTV use revenue or profit?
Gross profit. Using revenue inflates LTV by exactly your cost of goods and makes an unsustainable CAC look affordable. Some businesses go further and subtract ongoing support and servicing costs, which is more conservative and more honest.
Why does payback period matter if the ratio is healthy?
Because payback is a cash-flow constraint, not a profitability one. A strong LTV:CAC over three years still means you fund acquisition out of working capital until the money returns. A long payback caps how fast you can grow, regardless of how good the eventual return is.
How long should I wait before judging a campaign?
At least one full sales cycle, and preferably long enough for repeat purchases to register. Measuring a 90-day window on a business whose customers buy annually will show a loss on campaigns that are in fact profitable.
This calculator is an educational tool. Results are estimates based on the inputs you provide and do not constitute financial advice. Verify figures with your bank, broker or a qualified advisor before acting on them.