In Python, load the data with pandas and compute marketing efficiency ratio from column totals for the whole period, or row by row for each month. On the sample data it returns 4.22.
MER = Total revenue ÷ Total marketing spend
What you need
Marketing efficiency ratio (MER), also called blended ROAS, is total revenue divided by total marketing spend, with no attribution: every sale and every rupee of spend counts. You need these columns, here from the sample file monthly.csv:
- df["revenue"]: revenue (net of discounts)
- df["marketing_spend"]: marketing spend
Step by step
- Install pandas (pip install pandas) and save monthly.csv next to your script.
- Run the script. The first print shows one row per month, the second the figure for the whole period.
- To use your own data, rename your columns to match, or change the names in the code.
The code
import pandas as pd
df = pd.read_csv("monthly.csv")
# Each month
df["mer"] = df["revenue"] / df["marketing_spend"]
print(df[["month", "mer"]].round(2))
# Whole period: add up the parts first, then divide
mer_total = df["revenue"].sum() / df["marketing_spend"].sum()
print(round(mer_total, 2))
What you should get
Run against the sample data, the code above returns these values:
| Month | revenue | marketing_spend | mer |
|---|---|---|---|
| 2026-01 | 4,12,000 | 96,000 | 4.29× |
| 2026-02 | 4,38,500 | 1,02,000 | 4.30× |
| 2026-03 | 4,71,200 | 1,18,000 | 3.99× |
| 2026-04 | 4,55,800 | 99,000 | 4.60× |
| 2026-05 | 5,02,300 | 1,24,000 | 4.05× |
| 2026-06 | 5,48,900 | 1,31,000 | 4.19× |
| Whole period | 28,28,700 | 6,70,000 | 4.22× |
₹28,28,700 ÷ ₹6,70,000 = 4.22×
Notes for Python
- Dividing by zero in pandas does not raise an error: it gives inf or NaN. Check with df.replace([float("inf"), -float("inf")], float("nan")) before averaging or plotting.
- For the whole period, sum the columns first and then divide. df[col].mean() of the monthly results weights a small month the same as a large one.
- pct_change(), groupby() and resample() extend the same idea to weekly data, product categories and daily rows.
Where marketing efficiency ratio misleads
- MER includes revenue from returning customers and organic traffic, so it looks better at brands with loyal customers, whatever the ads do.
- It cannot tell you which channel works. Use it for the total and attribution for the split.
- Include every marketing cost, or the ratio is not comparable over time.
The full explanation, with a calculator, is on the Marketing efficiency ratio (MER) page.
Same metric, other tools
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About the data on this page
The figures come from a small made-up dataset, printed above in full so you can check every number by hand. Download it as monthly.csv. The results are computed from those rows when the page is built, and the Excel formulas, SQL and Python on these pages are run against the same rows before publishing, so the code and the answers agree.
To get these numbers from your own data without writing formulas, try AnalyzeIt: ask in plain words and it shows the working behind every figure.
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