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Product Management/growth-model-builder

Growth Model Builder

You need to model growth loops, levers, sensitivity analysis, and realistic projections.

A client needs to model their growth engine, understand which levers matter most, and build projections grounded in real metrics rather than wishful thinking.


How it works

  1. You provide the client name, business model, current metrics, growth channels, and assumptions
  2. The skill maps the growth loops, calculates viral and retention dynamics, models channel contributions, runs sensitivity analysis, and builds 3/6/12-month projections
  3. It returns a growth model Kate can use to pressure-test a client's growth plan, set realistic targets, and identify the highest-leverage interventions

Prompt

You are building a growth model for a Kate Makrigiannis consulting engagement. Kate uses this to help clients move from gut-feel growth expectations to a quantitative model they can actually steer. The model should be honest about uncertainty and explicit about which assumptions drive the numbers. Before writing, read knowledge/voice-tone-guide.md -- use the client-facing voice.

Inputs I will provide:

  • Client: {{CLIENT}} (company name, product, business model)
  • Current metrics: {{METRICS}} (users, revenue, MRR/ARR, retention rate, churn, conversion rates, ARPU -- whatever they have)
  • Growth channels: {{CHANNELS}} (how they acquire users today -- paid, organic, referral, sales, partnerships, etc.)
  • Assumptions: {{ASSUMPTIONS}} (growth rate expectations, planned channel investments, pricing changes, product launches, market size)
  • Context (optional): {{CONTEXT}} (stage, funding, team size, competitive dynamics, board expectations)

Step 1: Map the growth loops

Identify and diagram the client's active growth loops. Most businesses have 1-2 primary loops and several secondary ones.

Growth Loop Inventory

For each loop the business has (or should have):

Loop: [Name] (e.g., Paid Acquisition Loop, Viral/Referral Loop, Content/SEO Loop, Sales Loop)

  • Trigger: What starts the loop (ad impression, user invite, content publish, outbound email)
  • Steps: [Step 1] → [Step 2] → [Step 3] → [back to trigger]
  • Cycle time: How long one loop iteration takes (days/weeks/months)
  • Current strength: [Strong / Developing / Weak / Not yet active]
  • Compounding? Does this loop accelerate over time, or is it linear?
Loop Diagram:

[Acquisition] → [Activation] → [Retention] → [Referral/Revenue] ─┐
      ↑                                                            │
      └────────────────────────────────────────────────────────────┘

Draw a loop diagram for each active loop, showing where value feeds back into acquisition.

Step 2: Viral coefficient calculation

If the client has any referral or word-of-mouth channel, calculate the viral coefficient (K-factor):

Viral Dynamics

  • Invitations per user (i): X (average invites/shares per active user per [time period])
  • Conversion rate of invitations (c): X% (what percentage of invited people become users)
  • K-factor = i x c: X

Show the math: "K = {{i}} invitations x {{c}}% conversion = {{K}}"

Interpretation:

  • K > 1.0: True viral growth (each user brings in more than one new user). Rare and powerful.
  • K = 0.5-1.0: Viral amplification. Not self-sustaining, but meaningfully reduces CAC.
  • K < 0.5: Minimal viral contribution. Growth depends on paid/organic channels.
  • K = 0 or unknown: No referral mechanism. Flag as an opportunity.

Viral cycle time: X days (how long from user activation to their referral converting). Shorter cycle times amplify growth dramatically, even at the same K-factor.

Step 3: Retention curve analysis

Model how the client's user base retains over time. This is the foundation of the growth model: acquisition without retention is a leaky bucket.

Retention Model

Cohort PeriodUsers RemainingRetention RateNotes
Month 0X (100%)100%Acquisition cohort
Month 1XX%[Early drop-off assessment]
Month 3XX%[Activation quality signal]
Month 6XX%[Product-market fit signal]
Month 12XX%[Long-term retention floor]

If the client has cohort data, use it. If not, estimate from their stated churn rate and flag: [ASSUMPTION: retention curve estimated from stated monthly churn of X% -- actual cohort analysis may reveal different patterns (e.g., early churn concentrated in first 30 days)]

Churn and retention math:

  • Monthly churn rate = X%
  • Monthly retention rate = 100% - churn = X%
  • Annual retention = (monthly retention)^12 = X%. Show the calculation.
  • Average customer lifetime = 1 / monthly churn rate = X months

Retention quality assessment:

  • Flattening curve: Retention stabilizes after initial drop-off. Good sign for PMF.
  • Continuous decay: Retention keeps declining with no floor. Warning sign.
  • Smile curve: Retention dips then recovers (common with habit-forming products). Strong signal.

Step 4: Channel contribution model

Break down how each growth channel contributes to new user/customer acquisition.

Channel Mix

ChannelMonthly VolumeCAC% of New UsersScalabilityPayback Period
[Channel 1]X users$XX%[Linear / Compounding / Saturating]X months
[Channel 2]X users$XX%[Linear / Compounding / Saturating]X months
[Referral]X users$X (or $0)X%[Depends on K-factor]Immediate
TotalX users$X blended100%--X months blended

Payback period calculation: Payback = CAC / (ARPU x Gross Margin). Show the math for each channel.

Channel scalability assessment:

  • Linear: Paid channels. More spend = more users, but CAC tends to rise with scale.
  • Compounding: Content, SEO, community. Slow start but accelerating returns over time.
  • Saturating: Finite audience channels (specific communities, niche platforms). Will hit a ceiling.

Step 5: Sensitivity analysis

Identify the 3-5 variables that have the most impact on growth outcomes and model what happens when they change.

Key Lever Sensitivity

LeverBase CaseDownside (-20%)Upside (+20%)Impact on 12-Month Revenue
Monthly new usersXXX$X / $X
Activation rateX%X%X%$X / $X
Monthly retentionX%X%X%$X / $X
ARPU$X$X$X$X / $X
Viral coefficientXXX$X / $X

Show the math for each sensitivity scenario. For example: "If monthly retention improves from 92% to 95%, 12-month retention moves from 38% to 54%, increasing average lifetime from 12.5 to 20 months and LTV from $X to $X."

Highest-leverage lever: [Identify which single variable, if improved by 20%, produces the largest revenue impact.] This is where the client should focus optimization effort.

Step 6: Growth projections

Build month-by-month projections for 3, 6, and 12 months with three scenarios.

12-Month Growth Projection

Assumptions for each scenario:

  • Conservative: Current trends continue with no optimization. Channels grow at X%/month.
  • Base case: Planned optimizations succeed at 50% of expected impact. One new channel comes online.
  • Aggressive: All optimizations hit full targets. Two new channels contribute. Viral coefficient improves.
MonthConservative UsersBase UsersAggressive UsersConservative MRRBase MRRAggressive MRR
CurrentXXX$X$X$X
Month 3XXX$X$X$X
Month 6XXX$X$X$X
Month 12XXX$X$X$X

Show the projection math for at least Month 3 in the base case:

  • New users from channels: X (Channel 1) + X (Channel 2) + X (Referral) = X
  • Retained from prior months: X existing users x X% retention = X
  • Total users Month 3: X new + X retained = X
  • MRR: X users x $X ARPU = $X

Milestone Check

MilestoneConservativeBase CaseAggressive
1,000 users (or relevant milestone)Month XMonth XMonth X
$X MRRMonth XMonth XMonth X
[Client's stated target]Month X / Not reachedMonth XMonth X

Kate's Talking Points

  • The growth model's biggest risk: the single assumption that, if wrong, breaks the plan
  • The quick win: which lever has the highest sensitivity with the lowest effort to improve
  • The strategic question: is the client's growth plan realistic given retention dynamics, or are they planning to fill a leaky bucket?
  • If projections fall short of board/investor expectations, what specifically needs to change

For defining the North Star Metric this model should optimize toward, use /north-star-metric. For evaluating product-led growth readiness, use /plg-readiness-check. For diagnosing specific funnel stages within this model, use /funnel-analysis.


Example Output

Input

  • Client: Luma Health — a B2B SaaS platform that helps independent medical practices automate patient recalls, appointment reminders, and waitlist management. Subscription model, charged per provider seat.
  • Current metrics: 340 active practices (customers), $187K MRR, avg 3.2 provider seats per practice, ARPU $550/practice/month, monthly churn 3.1%, activation rate (practices sending first automated campaign within 14 days) 61%, referral rate ~18% of new signups cite word-of-mouth
  • Growth channels: Outbound SDR team (primary), Google Ads (secondary), EHR marketplace listings (early), word-of-mouth/referral (unstructured)
  • Assumptions: Plan to hire 2 more SDRs in Month 2, launch a structured referral program in Month 3, expect 15% MoM growth from sales team, EHR marketplace to contribute meaningful volume by Month 6
  • Context: Series A, 28-person team, $4.2M ARR run rate, board expects $7M ARR by end of year (~9 months), competitive pressure from two VC-backed rivals entering the independent practice segment

Output (abbreviated)

Growth Model: Luma Health

Prepared for Kate Makrigiannis | Engagement Use Only

The honest summary upfront: Luma's $7M ARR target is reachable in the base case — but it requires churn to stop getting worse, the referral program to actually launch and convert, and the SDR team to hit productivity faster than most sales hires do. Any two of those slipping means the board number is a Month 15 story, not Month 9.


Step 1: Growth Loop Inventory


Loop: Outbound Sales Loop

  • Trigger: SDR identifies independent practice via prospecting list or EHR data export
  • Steps: Outbound sequence → demo booked → trial/onboarding → paid seat → expansion (add providers) → practice refers peer → new prospect
  • Cycle time: 28–45 days (sales cycle for independent practices)
  • Current strength: Strong — this is the engine right now
  • Compounding? No. Linear. Each new SDR adds roughly linear volume. CAC doesn't improve without structural changes.
[SDR Outreach] → [Demo] → [Activation] → [Expansion (seats)] ──┐
      ↑                                                          │
      └──────────── [Referral to peer practice] ←───────────────┘

Loop: Word-of-Mouth / Referral Loop (Developing)

  • Trigger: Practice manager mentions Luma to another practice at a regional health conference, in a Facebook group, or to a referring physician
  • Steps: Happy customer mentions Luma → prospect visits site or contacts sales → converts → becomes new referral source
  • Cycle time: 45–90 days (relationship-driven, unstructured today)
  • Current strength: Developing — 18% of signups cite it, but there's no program amplifying it
  • Compounding? Yes, weakly — each satisfied customer is a potential node, but without a structured program the loop degrades quickly

Loop: EHR Marketplace Loop (Not Yet Active)

  • Trigger: Practice searches EHR app marketplace for recall/reminder tools
  • Steps: Listing impression → click → trial → paid conversion → review left on marketplace → new impression
  • Cycle time: 14–21 days (intent-driven, shorter cycle)
  • Current strength: Not yet active — listed but no volume yet
  • Compounding? Yes — reviews and ratings accumulate over time, improving organic ranking within the marketplace

Step 2: Viral Dynamics

K-factor Calculation

  • Invitations per customer (i): 0.6 referrals per practice per quarter (estimated from 18% of ~40 monthly new customers citing word-of-mouth, spread across installed base of 340)
  • Conversion rate (c): 31% (referral-sourced leads convert at roughly 1.5x the outbound rate of ~20%)
  • K = 0.6 × 0.31 = 0.19

[ASSUMPTION: invitation rate estimated from self-reported attribution — actual referral volume may be higher if some word-of-mouth isn't tracked through current attribution model]

Interpretation: K = 0.19 puts Luma in viral amplification territory, but on the low end. Referrals are reducing blended CAC modestly today, but this is not a self-sustaining loop. The planned referral program in Month 3 is the right call — even moving K from 0.19 to 0.35 would materially reduce dependence on outbound.

Viral cycle time: ~60 days (from activation to a referral converting). Shortening this — through an in-product referral prompt at peak satisfaction moments like first successful campaign — is the highest-leverage referral optimization.


Step 3: Retention Model

Monthly churn: 3.1% Monthly retention: 96.9% Annual retention: (0.969)^12 = 69.1% Average customer lifetime: 1 / 0.031 = 32.3 months

[ASSUMPTION: retention curve estimated from stated monthly churn of 3.1% applied uniformly — actual cohort analysis likely shows elevated early churn in months 1–2 among practices that never fully activated (39% of new customers miss the 14-day activation threshold)]

Cohort PeriodPractices RemainingRetention RateNotes
Month 0100100%Acquisition cohort
Month 19191%Early churn likely concentrated here — activation gap
Month 38585%Practices that activated are sticky; non-activators mostly churned
Month 67979%Flattening expected if activation problem is fixed
Month 126969%Reasonable floor given 3.1% blended churn

Retention quality assessment: The 61% activation rate is the warning sign. Practices that don't send their first automated campaign within 14 days are almost certainly in the early-churn bucket, and they're distorting the headline churn figure upward. Fix activation and the retention curve likely flattens meaningfully — which would have a larger impact on LTV than almost any other single intervention.


Step 4: Channel Mix

ChannelMonthly New CustomersCAC% of New CustomersScalabilityPayback Period
Outbound SDR28$1,84070%Linear3.3 months
Google Ads7$2,20017.5%Linear (saturating above ~$25K/mo spend)4.0 months
Word-of-mouth (unstructured)5~$180 (attribution cost only)12.5%Developing<1 month
EHR Marketplace0TBD0%CompoundingTBD
Total40$1,620 blended100%~3.0 months blended

Payback period math (SDR channel): Payback = $1,840 CAC ÷ ($550 ARPU × 85% gross margin) = $1,840 ÷ $467.50 = 3.9 months

Note: blended payback shown above uses a slightly different margin mix. SDR channel payback is closer to 3.9 months when calculated in isolation.

The referral channel is dramatically underutilized. At ~$180 effective CAC and sub-1-month payback, every referral customer is worth 10x a paid-acquisition customer in terms of capital efficiency. The structured referral program planned for Month 3 should be treated as a growth investment, not a marketing nicety.


Step 5: Sensitivity Analysis

Key Lever Sensitivity

LeverBase CaseDownside (−20%)Upside (+20%)12-Month MRR Impact
Monthly new customers40/mo