# Case: double marketing before exam season?

> Marginal CAC by channel, what a seasonal customer is worth and the cash a doubled marketing budget needs.

- Course: [Finance for Product People: From Unit Economics to Business Cases](https://productovi.com/courses/finance-for-product.md)
- Module: Does growth pay for itself?
- Lesson 20/32, ~40 min
- Source: https://productovi.com/courses/finance-for-product/marketing-budget-case

## Leo's exam-season plan

**Alex Tutor:** Exam season is coming at Klasna, and the product team, you included, is reviewing the marketing plan.

**Leo:** Exam season is our peak. For February to April 2027 I want to double marketing: 600,000 UAH a month instead of 300,000. Twice the spend, twice the families.

**Hanna:** Twice the spend, certainly. Twice the families, I doubt it. Last spring we tested every channel at four spend levels.

**Dataset (CSV):** [Last spring's channel tests](https://productovi.com/datasets/finance-for-product/marketing-budget-case/klasna-channel-tests.csv)

New families a month at four monthly spend levels per channel (average of February–April 2026).

- `channel`: paid_social, search or school_partnerships
- `monthly_spend_uah`: Spend on the channel in a month, UAH
- `new_families`: New paying families that spend brought in a month

**Sofia:** The current plan spends 150,000 on social, 90,000 on search and 60,000 on partnerships. That brings 50 + 34 + 26 = 110 families: a CAC of 300,000 / 110 = 2,727.27 UAH.

**Alex Tutor:** That is the average. Leo's question is about the second 300,000. Find each channel at double its current spend and add them up.

> **Exercise:** Use the dataset. How many new families a month would Leo's plan bring, with every channel at **double** its current spend (social 300,000, search 180,000, partnerships 120,000)?

**Alex Tutor:** Before we name the number, decide which one matters.

> **Exercise:** Today 300,000 UAH a month brings 110 families (average CAC 2,727.27). At 600,000 the tests show 166 families (average CAC 3,614.46). Which number should decide whether to spend the **extra** 300,000?

## Marginal CAC: what the extra hryvnia buys

**Sofia:** 166 − 110 = 56 more families for 300,000 more. That is 5,357 UAH for each extra family!

**Alex Tutor:** That is the **marginal CAC**, the cost of one more customer: extra spend divided by the extra customers it brings. The average only rises to 600,000 / 166 = 3,614.46 and hides it, because the first 300,000 still buys families at 2,727.

$$
CAC_{marginal} = \frac{\Delta \text{spend}}{\Delta \text{customers}} = \frac{600\,000 - 300\,000}{166 - 110}
$$

*Decide on the extra spend by what the extra customers cost, not by the average.*

**Hanna:** Channels saturate. Social shows the ad to the same parents again; search runs out of people searching that week.

**Alex Tutor:** And not every channel saturates at the same speed. Check them one by one.

> **Exercise:** Use the dataset. What is the **marginal CAC** of doubling **search** from 90,000 to 180,000 UAH a month?

**Alex Tutor:** Line the channels up side by side.

> **Exercise:** Match each change in spend to the marginal CAC of the families it adds (use the channel tests).

## What a spring family is worth

**Sofia:** Is 5,357 too much? That depends on what a spring family leaves us.

**Hanna:** Exam families are their own crowd. They study about seven maths lessons a month until the exams at the end of May, which leaves us about 1,400 UAH a month. Then most stop.

**Hanna:** About 30% come back in September and leave around 2,000 each over the autumn. That adds 0.3 × 2,000 = 600 to every spring family.

**Alex Tutor:** Try one start month yourself before the table.

> **Exercise:** An exam family leaves about 1,400 UAH of contribution margin for each month it studies, from its start month until the exams at the end of May. About 30% of spring families return in September and leave 2,000 each. What is one family that starts in **March** worth?

**Alex Tutor:** So a family's value depends on when it starts. February: four months to the exams, 4 × 1,400 + 600 = 6,200. March: 4,800. April: only 3,400.

> **Value of one spring family by start month**
>
> | Starts in | Months to the exams | Until the exams | September return | Value |
> |---|---|---|---|---|
> | February | 4 | 5,600 | 600 | **6,200** |
> | March | 3 | 4,200 | 600 | **4,800** |
> | April | 2 | 2,800 | 600 | **3,400** |
>
> UAH of contribution margin: 1,400 per month of study; 30% return in September with 2,000 each.

**Leo:** So an April family is worth barely half of a February one.

> **Exercise:** Leo's plan pays a marginal CAC of 5,357.14 UAH for every extra family. In which start months is an extra family worth **more** than that?

## The plan in cash

**Alex Tutor:** Now the whole plan. 300,000 extra a month for three months is 900,000. The extra 56 families a month are worth 56 × (6,200 + 4,800 + 3,400) = 806,400. Net: **−93,600 UAH**.

**Hanna:** And the bank account sees it in a different order. The ad money leaves each month in full; each extra family brings 1,400 a month while it studies.

**Sofia:** So in February 56 families bring 78,400 against 300,000 out. In March there are 112 of them, in April 168.

**Alex Tutor:** Keep a running total from February. Where is it lowest?

> **Exercise:** What is the **lowest cumulative cash** of Leo's extra spend (300,000 UAH a month in February–April; 56 extra families each month, each bringing 1,400 UAH a month until the end of May)? Enter it as a negative number.

## Channel by channel

**Hanna:** The low point comes at the end of April, right before the summer, when our lessons drop anyway. And September never closes the gap.

**Alex Tutor:** Now test the one channel that still looked cheap.

> **Exercise:** Klasna doubles only school partnerships, from 60,000 to 120,000 UAH a month, in February, March and April. Use the channel tests for the extra families a month and the value of a spring family by start month. What is the **net value** of this change (value of the extra families minus the extra spend)?

**Alex Tutor:** But the channels differ. Partnerships add an extra family for 2,857, below even an April family's 3,400. Doubling them: 21 families × 14,400 = 302,400 of value for 180,000. **+122,400.**

**Alex Tutor:** Doubling social loses 133,200, and search 82,800. Together that's the −93,600: one good channel hidden under two bad ones.

**Leo:** Can schools even take twice the partnerships?

**Sofia:** The test went up to 120,000, so the data covers it. But partnerships take time to set up; they would need to start in January.

> **Exercise:** In 2–4 sentences: which part of Leo's plan would you keep, and why? Use marginal CAC by channel and the value of a spring family.

## The memo for Leo

**Leo:** Board call on Monday. One answer: do we double marketing before exam season?

**Hanna:** Answer from the tests, not from the average: marginal CAC, what a spring family is worth, and the cash the plan needs.

**Alex Tutor:** And end with a verdict Leo can act on: yes, no, or yes if. For "yes if", name the conditions.

**Sofia:** A short memo, then. Numbers first, verdict at the end.

> **Exercise:** Write the memo for Leo: double marketing in February–April 2027?

> **Key ideas**
>
> - Judge extra spend by **marginal CAC** (extra spend ÷ extra customers), not the average: doubling to 600,000 brings 56 more families at 5,357.14 each, while the average only rises to 3,614.46.
> - Channels saturate at different speeds: partnerships 2,857.14 per extra family, social 6,818.18, search 6,923.08.
> - A seasonal customer's value depends on when they start: 6,200 (February), 4,800 (March), 3,400 (April).
> - The whole plan: 900,000 for 806,400 of value, −93,600; partnerships alone +122,400.
> - In cash the plan bottoms out at −429,600 at the end of April and never fully recovers.
> - Split a plan by channel and by month before you approve it as a whole.

**Alex Tutor:** That's the module in one case: what a customer leaves, what the next one costs, and how long the bank account has to wait in between.

- Previous lesson: [Overtrading: why fast growth eats cash](https://productovi.com/courses/finance-for-product/growth-eats-cash.md)
- Next lesson: [Time value of money: why a hryvnia next year is worth less](https://productovi.com/courses/finance-for-product/time-value-of-money.md)

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