Lesson 7.1 · 50 minAdvertising fundamentals and the numbers

What you will have

The student has docs/ads-plan.md stating a test budget, a target cost per lead and a stop rule, backed by a calculator page in the admin area filled with their own figures.

Video

The video for this lesson is not recorded yet.

Prompts used in this lesson

Part 7 — Demonstration: the calculator page

Purpose: I am about to start paid advertising and need a calculator in the admin
area to work out what I can afford to pay for a lead.

Context: This is the brightside-site project. The admin area lives under /admin and
is protected by the existing login. Follow the page and component patterns already
used by /admin/today, and the styles in docs/design.md.

Build a page at /admin/ads-calculator with these inputs:
- gross profit per customer
- share of that profit I am willing to spend to win a customer (percent)
- share of leads that become customers (percent)
- share of visitors that become leads (percent)
- test budget per platform
and these outputs, updating as I type:
- maximum cost per customer
- target cost per lead
- affordable cost per click
- number of leads and clicks the test budget buys at those targets
- return on ad spend at the target, given an optional "revenue per customer" input.
Show the formula under each output in plain words. Add a link to the page in the
admin navigation.

Constraints: no database changes; keep the values in the browser's local storage so
they survive a reload. All inputs start empty - do not pre-fill example numbers.
Handle empty and zero inputs without errors. The page must not be reachable without
logging in.

Done when: the build passes, you have loaded the page while logged in, entered a set
of values and confirmed each output by hand calculation, and confirmed that the page
redirects to the login when logged out. Report what you checked.

Part 8 — Demonstration: writing the plan

Purpose: write docs/ads-plan.md, the plan I will follow before and during my first
ad campaigns.

Context: read docs/brief.md for the business and docs/measurement-plan.md for how
leads are measured. My figures from the calculator are: [paste your five inputs and
the outputs]. My decisions: test budget of [amount] per platform over [number] days
on Google Search and on Meta; stop rules: [your sentences].

The document must contain: the figures and where each came from (measured or
estimated); target cost per lead; affordable cost per click; test budget per platform
and the daily amount it implies; the stop rules, word for word; a short list of what
I will check and on which days; and a line stating that estimated figures will be
replaced with measured ones after the first week.

Constraints: one page. Use only the numbers I gave you - do not add benchmarks,
industry averages or forecasts. If something needed is missing, ask me.

Done when: the file exists, every number in it traces to my input, and you have
re-checked the arithmetic.

Do along

Pause the video where told and do each step on your own project.

1. Start from lesson-6.9. After Part 7, pause: run the calculator prompt unchanged.
2. Work out your own customer value. If you have no history, write down your assumption and mark it "estimate".
3. Take your close rate from the CRM pipeline (won leads divided by all leads that reached a final stage). With too few leads, estimate and mark it.
4. Enter your figures in /admin/ads-calculator. Change the conversion rate up and down and watch how the affordable click moves.
5. Decide your test budget per platform and write two stop rules in full sentences with amounts.
6. After Part 8, pause: run the plan prompt with your figures in the brackets.
7. Commit: git add -A, then git commit -m "Lesson 7.1: ads calculator and ads plan", then git push.

Check your work

1. Open /admin/ads-calculator logged in: outputs update as you type. Logged out: you are sent to the login.
2. Check one output by hand: target cost per lead equals maximum cost per customer multiplied by your close rate.
3. Open docs/ads-plan.md and find three things: a test budget as an amount, a target cost per lead as an amount, and at least one stop rule that names a trigger and an action. If any is missing or vague ("stop if results are poor"), rewrite it.

Common problems

• Outputs show "NaN" or "Infinity" → an empty or zero input is being divided. Tell Claude: "Outputs must show a dash when an input is empty or zero; fix and test with empty fields."
• The affordable click looks impossibly low → usually a percent entered as a fraction (0.05 instead of 5) or the reverse. Ask Claude to label each field with its unit and an example of the format.
• The plan contains numbers you never supplied → Claude filled gaps. Tell it: "Remove every figure I did not give you and list what you need from me instead."

Homework

About 30 minutes, on your own, after the lesson. No later lesson depends on it.

1. Three scenarios. In the calculator, keep your customer value and change the two rates: a cautious case, your expected case and a hopeful case. Deliverable: a "Scenarios" table in docs/ads-plan.md with the target cost per lead and affordable cost per click for each. Done when: the table has three rows and one sentence says how many leads the test budget buys in the cautious case.
2. Check one estimate against your records. Go through your last ten real enquiries (messages, calls, invoices) and count how many became customers. Deliverable: that count written beside the close rate in the plan, labelled "from records". Done when: the plan shows both the figure you used and the counted one. With no past enquiries, write "no history yet".
3. Stop-rule drill. Apply your stop rules to two imagined days: the campaign has spent twice your target cost per lead and brought one lead; half the budget is gone and leads cost double the target. Deliverable: your action for each, in one sentence, under "Stop-rule drill" in the plan. Done when: each answer follows from the written rules without a new decision. If one does not, tighten that rule's wording.

If a task changed files in the project, commit and push without a tag: git add -A, git commit -m "Homework 7.1", git push.