Cash flow projection: cohort payback and the cash cost of growth

The formula

Each month acquires a cohort sized by your month-1 spend, CPA, and compounding monthly growth rate. Every acquired customer buys once in the acquisition month; in month N afterward, the share of the cohort reordering follows a 12-month repeat-rate curve. Two presets ship with the tool: a DTC ecommerce curve starting at 25% in the second month and decaying to 2.5% by month 13, and a higher, flatter subscription curve starting at 68%, blendable by your subscription attach rate.

Cash per cell is gross margin minus acquisition cost. From the grid: each cohort's payback month, the account's cumulative break-even month, the peak cash deficit and when it hits, and an LTV buildup with LTV to CAC. A binary search finds the maximum monthly growth rate whose peak deficit still fits inside your cash ceiling. Optional toggles model CPA escalation compounding per cohort and untracked lift discounting your blended CPA.

Expected input

No CSV. Core inputs: AOV, blended new-customer CPA, gross margin, month-1 ad spend, monthly growth rate, projection length (6 to 24 months), and your maximum cash outlay. All 12 monthly repeat rates are editable, first-order AOV and margin can be split from repeat, and the LTV Analysis tool can prefill everything from your actual order data. Scenarios encode into a shareable URL.

Assumptions and limits

• –Cash is gross margin only: no fixed costs, refunds, or payment-timing effects, and cash lands the month the order happens.
• –Repeat behavior ends after the 12-entry curve, so cohorts older than 13 months contribute nothing in longer projections.
• –Each customer orders at most once per month, and cohort sizes round to whole customers.
• –LTV to CAC compares the month-1 cohort's curve against each later month's escalated CPA.