Modeling client lifetime value when engagements are irregular and unpredictable

# Modeling client lifetime valuelifetime valueLifetime Value: the total revenue (or profit) a customer generates throughout their entire relationship with your business.Voir la définition complète → when engagements are irregular and unpredictable

An accounting firm signs a mid-market manufacturer for a $15,000 annual audit. The client goes quiet for two years, no calls, no upsells, nothing. Then they call back needing due diligence support for an acquisition: a $75,000 mandate, five times the original retainer. A subscription-business LTVLTVLifetime Value: the total revenue (or profit) a customer generates throughout their entire relationship with your business.Voir la définition complète → (lifetime valuelifetime valueLifetime Value: the total revenue (or profit) a customer generates throughout their entire relationship with your business.Voir la définition complète →) model would have written this client off after month 13 of silence. That model is wrong for professional services, and using it will make you underinvest in your best long-term relationships.

This lesson builds an LTVLTVLifetime Value: the total revenue (or profit) a customer generates throughout their entire relationship with your business.Voir la définition complète → approach suited to lumpy, mandate-driven client relationships: law firms, accounting practices, consultancies, agencies.

Why the SaaS LTVLTVLifetime Value: the total revenue (or profit) a customer generates throughout their entire relationship with your business.Voir la définition complète → formula breaks here

The standard formula you'll see everywhere:

LTV = (Average Revenue per Account × Gross Margin %) / Churn Rate

This assumes steady, periodic revenue (monthly subscriptions) and a stable churn ratechurn rateChurn rate is the percentage of customers or revenue lost over a period. It measures how fast a business loses its existing customer base.Voir la définition complète → (the percentage of customers who stop paying each period). Neither holds in professional services.

A client isn't "churned" just because they haven't engaged you in 18 months. They might be between mandates. A general counsel who hired your law firm for one litigation matter isn't gone, they're dormant until the next dispute arises. Treating dormancy as churn understates true relationship value and can push firms to cut nurture spend on accounts that are actually appreciating.

The core shift: think in engagement probability, not renewal rate

Instead of asking "will this client renew," ask two separate questions:

1. What's the probability this client re-engages us in a given period?

2. Given re-engagement, what's the expected size of that mandate?

This is the logic behind probabilistic customer lifetime models used in retail and telecom, notably the BG/NBD model (Beta-Geometric/Negative Binomial Distribution) popularized by Fader and Hardie for modeling irregular purchase behavior. You don't need to build the full statistical model to borrow its mindset: separate *frequency* from *monetary value*, and model both as distributions, not constants.

Building blocks for a professional services LTVLTVLifetime Value: the total revenue (or profit) a customer generates throughout their entire relationship with your business.Voir la définition complète →

1. Engagement frequency rate

Look at your historical client base over 3 to 5 years. For clients acquired more than 3 years ago, what share generated at least one new mandate in years 2, 3, 4, 5? This gives you a re-engagement curve instead of a single churn number.

Example: a boutique M&A advisory firm might find 40% of clients return within 24 months, another 15% return between 24 and 48 months, and the rest never return. That's a frequency distribution, not a flat rate.

2. Expansion multiplier

Track mandate size on second and third engagements versus the first. In professional services, repeat mandates are frequently *larger* than the original, because trust is established and scope expands (audit becomes audit plus tax plus advisory).

Estimate (illustrative, based on common patterns cited in professional services benchmarking by firms like Hinge Research Institute): repeat engagements in B2B professional services average 1.3x to 2x the value of the initial engagement, though this varies enormously by practice area.

3. Relationship horizon

Instead of a decay curve, use an observed horizon: how many years does the average client relationship stay "live" (capable of producing a mandate) before genuinely going cold (firm sold, business closed, relationship contact departed)? For many B2B professional services firms this horizon runs 7 to 10 years, far longer than the gaps between individual mandates.

A worked example

Let's model a mid-sized accounting firm's client.

• Initial engagement value: $20,000
• Probability of re-engagement in any given year (based on historical cohort data): 25%
• Expansion multiplier on repeat engagements: 1.5x
• Relationship horizon: 8 years
• Gross marginGross marginGross margin is the share of revenue left after subtracting the direct cost of producing goods or services, expressed as a percentage of revenue.Voir la définition complète → on services: 35% (typical range for professional services firms, estimate)

Expected number of re-engagements over 8 years = 0.25 × 8 = 2 (simplified expected value, ignoring compounding effects for clarity)

Expected value per re-engagement = $20,000 × 1.5 = $30,000

Total expected revenue = $20,000 (initial) + (2 × $30,000) = $80,000

Apply gross margingross marginGross margin is the share of revenue left after subtracting the direct cost of producing goods or services, expressed as a percentage of revenue.Voir la définition complète →: $80,000 × 0.35 = $28,000 expected gross profit LTV

Compare this to a naive model that assumes the client is "lost" after 18 months of silence and only counts the initial $20,000 engagement at 35% margin: $7,000. The probabilistic model shows the true relationship is worth 4x more. That gap is the entire argument for investing in long-term account nurture (newsletters, check-ins, invitations to firm events) even during quiet periods.

What this changes about CACCACCustomer Acquisition Cost (CAC) is the total sales and marketing spend divided by the number of new customers gained in a period. It measures how efficiently you grow.Voir la définition complète → payback and marketing spend

CACCACCustomer Acquisition Cost (CAC) is the total sales and marketing spend divided by the number of new customers gained in a period. It measures how efficiently you grow.Voir la définition complète → (customer acquisition costcustomer acquisition costCustomer Acquisition Cost (CAC) is the total sales and marketing spend divided by the number of new customers gained in a period. It measures how efficiently you grow.Voir la définition complète →: total sales and marketing spend divided by new clients won) looks unaffordable if you only measure it against first-engagement revenue.

If a law firm spends $8,000 in business development cost (partner time, proposals, pitch events) to win a client whose first mandate is $20,000 at 35% margin, apparent gross profit from that engagement is $7,000, a thin payback. But against the $28,000 lifetime estimate above, CACCACCustomer Acquisition Cost (CAC) is the total sales and marketing spend divided by the number of new customers gained in a period. It measures how efficiently you grow.Voir la définition complète → payback is comfortable and justifies more aggressive acquisition spend on the right client profile.

This is why professional services firms that only track first-year ROIROIReturn on Investment: the ratio of net profit to the cost of an investment. A 300% ROI means each dollar invested returns $3.Voir la définition complète → on business development chronically underinvest in relationship-based marketing (thought leadership, alumni networks, referral cultivation) that pays off on a 3 to 7 year horizon.

Segment before you model

Don't build one LTVLTVLifetime Value: the total revenue (or profit) a customer generates throughout their entire relationship with your business.Voir la définition complète → number for the whole firm. Segment by:

• Practice area (litigation mandates are lumpier than recurring compliance work)
• Client size (enterprise clients have longer horizons and higher expansion multipliers than small business clients)
• Referral source (referred clients often show higher re-engagement rates than cold-acquired ones, per patterns commonly cited in professional services marketing research from sources like the Professional Services Council and Hinge Research Institute)

A firm that averages these together will misallocate budget toward whichever segment looks best on a blended, misleading number.

Data you actually need to track

To run this model with real numbers instead of guesses, your CRMCRMCustomer Relationship Management: software and strategy to manage and analyse customer interactions throughout their lifecycle.Voir la définition complète → (customer relationship managementcustomer relationship managementCustomer Relationship Management: software and strategy to manage and analyse customer interactions throughout their lifecycle.Voir la définition complète → system) needs to capture, at minimum:

client_id, engagement_start_date, engagement_end_date,
engagement_value, practice_area, referral_source,
is_repeat_engagement (boolean), prior_engagement_value

Most firms have this data scattered across billing systems, partner spreadsheets, and memory. The first practical step isn't sophisticated modeling, it's consolidating engagement history into one queryable table. Firms using practice management software (Clio for law, Karbon or Practice Ignition for accounting) often already have this, just unused for marketing analysis.