MK-066 | Working backward to target cost per add-to-cart
For a regular chat, upload packs/mk-066.md. It includes the shared rules, this method, and required references
Purpose
This skill delivers: Cost derived from the add-to-cart purchase rate and CPA
Recalculability does not mean the data is complete; break-even points and cost ceilings apply only under the stated assumptions
Required inputs
Raw inputs: per-valid-order Target CPA, matched add-to-carts A and resulting valid purchases P, event/person/order units, matching method, mature window and actual add-to-cart spend
Method
- Fix Target CPA and valid-order definition; specify whether cost concerns events, cart users or deduplicated cart flows. Match subsequent valid purchases to those carts rather than divide unrelated purchase and cart events
- For a matched cohort/window, cart-to-purchase ratio is P/A. If the ratio counts people but Target CPA counts orders with multiple orders per person, obtain consistent order/flow units first. Unmatched or immature outcomes leave the usable ratio pending
- With A positive and consistent units, target add-to-cart cost = Target CPA × P/A. Compare matched spend/A in the same unit. Values outside the defined feasible ratio require duplicate/unit checks rather than clamping to 100%
- With A zero, the ratio is undefined. With A positive and P zero, observed ratio/formula value zero supports no positive cart allowance; retain actual spend and do not call purchase cost zero
- Actual matched cart cost above target identifies cost/completion gaps. Use checkout/payment evidence to choose landing repair or acquisition changes. Recompute and withdraw obsolete judgments after purchases, refunds, matching or Target CPA changes
Calculations and interpretation
Hypothetical check: Target CPA 216 with 100 deduplicated cart flows and 25 valid orders gives target cart cost 54. Confirming 50 mature orders changes it to 108. Retain ratio, currency and units with the calculation; this task delivers add-to-cart cost
Decision rules authored by ThinkWithBlack on 2026-10-14; original course sources are retained below
Required output fields
| Order | Field | How to complete |
|---|---|---|
| 1 | Input variable | Use source evidence, an intermediate method result, or an explicit unknown; do not invent information |
| 2 | Value | Use source evidence, an intermediate method result, or an explicit unknown; do not invent information |
| 3 | Unit and definition | Use source evidence, an intermediate method result, or an explicit unknown; do not invent information |
| 4 | Source | Use source evidence, an intermediate method result, or an explicit unknown; do not invent information |
| 5 | Formula | Use source evidence, an intermediate method result, or an explicit unknown; do not invent information |
| 6 | Result | Use source evidence, an intermediate method result, or an explicit unknown; do not invent information |
| 7 | Limitations | Use source evidence, an intermediate method result, or an explicit unknown; do not invent information |
Verification cases
MK-066-C05 | A required denominator is zero
Expected: Report that the formula is undefined; do not output a zero cost or an infinite target
MK-066-C06 | Only some costs are supplied
Expected: Retain the partial result and excluded items; do not call it complete profitability
Method sources
Source file: Meta廣告學程 104 廣告的數據決策
Location: Add to cart
Source basis: extracted from course materials
Source URL: https://docs.google.com/presentation/d/16FiqnSxBs-gSDxsxUBNhWdUX5vZrIWoZPGangj_f_Pk/edit
English translation of source excerpt:
Today's add-to-cart completion rate = 30%, meaning an order requires 3.3 adds to cart. Completing an order costs 450, so each add to cart carries 450 / 3.3 = NT$136
