Model how creative performance changes your payback period — then solve backwards from the payback target to the CPI and D7 ROAS your team can actually test against next week.
Verdict
Contribution LTV/CAC of 2.11× leaves you whole in month 9. A 29% rise in CPI drops you to 1.5× and pushes payback out materially. This is a business that needs its creative refreshed, not one that can coast.
Cumulative payback
M9
First profitable month: M5. Cumulative zero crossed in month 9.
Contribution LTV / CAC
2.11×
$5.28 kept per $2.50 spent
Deepest cash trough
-$247k
Deepest point in month 4. The cash you need before you start, not the profit you end with.
Steady-state monthly profit
$86k
Reached once all 8 cohorts are stacked, from month 8.
What one install is worth, and what it costs.
Revenue LTV
$6.72
3% pay × $28/mo × 8 mo
Revenue-related cost
$1.44
15% store + 5% rewards + $0.10/install
Contribution LTV
$5.28
What one install actually keeps
CAC
$2.50
Your CPI
Same budget every month. The line crosses zero the month you have paid back everything spent to date.
One cohort of installs, tracked from the day you bought them. Revenue ROAS is what your dashboard shows. Contribution ROAS is what your bank account sees.
Everything else held constant. Only CPI moves.
| CPI | vs today | Installs / mo | LTV / CAC | Payback | Steady profit / mo |
|---|---|---|---|---|---|
| $1.50 | −40% | 66,667 | 3.52× | M5 | $227k |
| $2.00 | −20% | 50,000 | 2.64× | M7 | $139k |
| $2.50today | — | 40,000 | 2.11× | M9 | $86k |
| $3.00 | +20% | 33,333 | 1.76× | M13 | $51k |
| $3.75 | +50% | 26,667 | 1.41× | Never | $16k |
| $5.00 | +100% | 20,000 | 1.06× | Never | -$19k |
Payback does not move in a straight line with CPI. A 20% improvement to $2.00 pulls payback from M9 in to M7; a 50% deterioration to $3.75 stops it paying back inside 24 months entirely. The further you sit from a healthy multiple, the more each cent of CPI costs. Note the $3.75 row: LTV/CAC is still 1.41× — every install is individually profitable — yet the company never pays back, because a thin margin cannot carry $25k/mo of fixed cost. Unit economics working is not the same as the business working.
Constant monthly budget, cohorts stacking to steady state.
| Month | Installs | Revenue | Ad spend | Fixed | Rev. cost | Profit | Cumulative |
|---|---|---|---|---|---|---|---|
| M1 | 40,000 | $34k | $100k | $25k | $11k | -$102k | -$102k |
| M2 | 40,000 | $67k | $100k | $25k | $17k | -$75k | -$177k |
| M3 | 40,000 | $101k | $100k | $25k | $24k | -$48k | -$226k |
| M4 | 40,000 | $134k | $100k | $25k | $31k | -$21k | -$247k |
| M5 | 40,000 | $168k | $100k | $25k | $38k | $5k | -$242k |
| M6 | 40,000 | $202k | $100k | $25k | $44k | $32k | -$210k |
| M7 | 40,000 | $235k | $100k | $25k | $51k | $59k | -$150k |
| M8 | 40,000 | $269k | $100k | $25k | $58k | $86k | -$64k |
| M9 | 40,000 | $269k | $100k | $25k | $58k | $86k | $22k |
| M10 | 40,000 | $269k | $100k | $25k | $58k | $86k | $108k |
| M11 | 40,000 | $269k | $100k | $25k | $58k | $86k | $194k |
| M12 | 40,000 | $269k | $100k | $25k | $58k | $86k | $280k |
| M13 | 40,000 | $269k | $100k | $25k | $58k | $86k | $366k |
| M14 | 40,000 | $269k | $100k | $25k | $58k | $86k | $452k |
| M15 | 40,000 | $269k | $100k | $25k | $58k | $86k | $538k |
| M16 | 40,000 | $269k | $100k | $25k | $58k | $86k | $624k |
| M17 | 40,000 | $269k | $100k | $25k | $58k | $86k | $710k |
| M18 | 40,000 | $269k | $100k | $25k | $58k | $86k | $796k |
It's already computed from your numbers — it's just behind this glass. Drop your work email and it unlocks instantly, forever.
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Most UA dashboards answer “what was my ROAS?”. This tool answers the question your CFO actually asks: when is the whole programme cash-positive — ad spend, fixed cost, store fees and all. It runs a month-by-month P&L where every cohort you buy stacks its revenue over its paying lifetime, and tracks the cumulative line until it crosses zero.
The Solve backwards mode inverts the model: pick the month you need to be whole, and it derives the maximum CPI that gets you there — then converts it into a D7 revenue ROAS kill line your creative team can test against within a week. The Cost of doing nothing mode compounds a realistic 6–10%/mo CPI drift to show what an unrefreshed creative set quietly costs over a year, on identical spend.
New to payback maths? Start with our guides on the app payback period and the D7 ROAS kill line. For the inputs, sanity-check your assumptions against our CPI benchmarks and retention benchmarks, or get a quick single-cohort view in the ROAS calculator.
The number of months until the cumulative profit of your user acquisition programme returns to zero — every dollar of ad spend, fixed cost and revenue-related cost paid back by cohort revenue. It's a stricter and more honest metric than per-cohort ROAS, because it includes fixed costs and the cash trough you have to finance along the way.
Because dashboards show revenue ROAS, not contribution. Store fees (typically 15–30%), rewards, refunds and per-install variable costs sit between revenue and your bank account. Depending on your cost structure, true break-even usually sits at 120–140% revenue ROAS.
Ad creatives fatigue: as frequency builds, CTR falls and the auction charges you more for the same install. At scale on Meta and TikTok, CPI on an unrefreshed creative set typically drifts up 6–10% per month. Compounding for a year, that quietly doubles your acquisition cost — which is why the Cost of doing nothing view usually shocks people.
Because a cohort revenue curve has a roughly fixed shape, an early ROAS reading predicts the endpoint. The tool derives the day-7 revenue ROAS a creative must clear for your payback target to stay alive — below it, kill the creative and move budget. Re-derive the multiple from your own cohort data before trusting it.
A planning model, not a financial forecast. Revenue is modelled as a flat monthly contribution per paying user across the paying lifetime, then zero — retention drives the shape of that lifetime, not a month-by-month decay curve. Fixed cost does not scale with budget. Replace every default with your own numbers before making a decision on them.