Core Marketplace Metrics: Precise Definitions
Marketplace businesses use a distinct vocabulary of metrics that differ from SaaS. Imprecise use of these terms in investor materials or board reports is a red flag that the management team does not have full command of their own business model. Here are the key metrics with precise definitions.
How to Model a Marketplace P&L
The marketplace P&L is structured differently from a SaaS P&L. The most important distinction is at the top line: marketplace revenue is the take rate applied to GMV, not the full GMV figure. A marketplace that facilitates £100m of GMV annually is not a £100m revenue business; if its take rate is 12%, it is a £12m revenue business. This distinction is fundamental and must be clear in all investor communications.
| Line Item | Formula / Note | Example (£m) |
|---|---|---|
| Revenue | ||
| GMV | Active buyers × AOV × transaction frequency | £100.0m |
| Take rate | Net revenue / GMV | 12.0% |
| Net revenue | GMV × take rate | £12.0m |
| Cost of Revenue | ||
| Payment processing costs | ~1.5–2.5% of GMV for card payments | (£1.8m) |
| Fraud losses | Typically 0.1–0.3% of GMV | (£0.15m) |
| Buyer and seller support (variable) | Per-transaction cost, volume-driven | (£0.6m) |
| Gross profit | Net revenue minus variable COGS | £9.45m |
| Gross margin | Gross profit / net revenue | 78.8% |
| Operating Expenses (largely fixed) | ||
| Buyer acquisition (marketing) | Buyer CAC × new buyers acquired | (£4.0m) |
| Seller acquisition and success | Seller CAC × new sellers acquired | (£1.5m) |
| Product and engineering | Fixed headcount cost | (£3.0m) |
| G&A | Fixed overhead | (£1.2m) |
| EBITDA | (£0.25m) | |
The key inflection point in a marketplace model is when contribution margin turns positive. Contribution margin is gross profit minus variable acquisition costs (buyer and seller CAC for the current cohort). Before contribution margin is positive, every incremental transaction destroys value because the variable cost of acquiring the parties to that transaction exceeds the gross profit from it. Once contribution margin is positive, the fixed cost base (product, engineering, G&A) is the only remaining drag on EBITDA, and the path to profitability is clear.
Unit Economics: Both Sides
Marketplace unit economics are more complex than SaaS unit economics because they are two-sided. You must model buyer CAC and buyer LTV separately from seller CAC and seller LTV, and you must understand how the two sides interact.
Buyer Unit Economics
Buyer LTV is driven by three variables: average gross profit per transaction (AOV × take rate × gross margin), transaction frequency (how often a buyer transacts per year), and buyer retention (what proportion of buyers transact in year two, year three, etc.). A worked example: a marketplace with £150 AOV, 12% take rate, 78% gross margin, three transactions per year, and 65% annual retention generates:
- Gross profit per transaction: £150 × 12% × 78% = £14.04
- Year 1 gross profit: £14.04 × 3 transactions = £42.12
- LTV (3-year, discounting at 10%): approximately £85 to £95 depending on assumptions
- If buyer CAC is £30, LTV:CAC ratio is approximately 3x — solid but not exceptional
Seller Unit Economics
Seller unit economics are often treated as an afterthought in marketplace financial models, but they are the foundation of the business. A marketplace is only as good as its supply side: if sellers are not economically incentivised to remain on the platform, buyer experience deteriorates and GMV follows.
Seller LTV is driven by the seller's GMV contribution (how much GMV they bring to the platform), the take rate applied to that GMV, and seller retention. A seller who generates £50,000 of GMV annually at a 12% take rate contributes £6,000 of net revenue per year. If seller CAC is £500, the payback period is less than one month — sellers are typically far more efficient to acquire than buyers, but they also require ongoing management, support and incentives to remain active.
"In most marketplace failures, the supply side breaks first. Buyers are easier to acquire and quicker to notice when supply thins out. A marketplace that obsesses over buyer CAC and ignores seller retention is building on a foundation that can collapse without warning. Both sides of the LTV:CAC calculation matter equally."
Marketplace Liquidity Economics
Liquidity is the defining operational metric of a marketplace: the probability that a buyer who arrives on the platform can find and successfully transact with a seller who meets their requirements. Low liquidity means buyers leave unsatisfied, demand-side retention falls, and the marketplace begins to lose credibility on both sides simultaneously.
The liquidity flywheel works as follows: more active buyers attract more sellers (because the addressable market for sellers is larger); more active sellers improve selection and choice for buyers; better selection improves buyer satisfaction and transaction frequency; higher transaction volume increases take rate revenue, which funds better buyer and seller acquisition. Each loop reinforces the others, and the compounding rate of this flywheel is the single strongest predictor of long-term marketplace defensibility.
Take Rate Dynamics
The take rate is not a fixed number. It is a strategic variable that responds to competitive intensity, the value the marketplace adds to each transaction, and the mix of transaction types in the GMV base.
Take rate expansion is driven by: adding value-added services that generate additional fees (insurance, financing, logistics, trust and verification); increasing payment processing margin (switching from marketplace to managed payments); moving up-market to higher-value transactions where absolute fees are more palatable; and reducing the competitive set through network effect moats.
Take rate compression is driven by: new entrant marketplaces with lower fees using price to acquire share; large buyers or sellers threatening to build or join alternative platforms; regulatory scrutiny of marketplace fees (particularly in financial services categories); and GMV mix shifts towards lower-margin categories.
Year 1: £10m GMV × 10% take rate = £1m net revenue
Year 2: £25m GMV × 11% take rate = £2.75m net revenue
Year 3: £55m GMV × 12% take rate = £6.6m net revenue
The take rate expansion from 10% to 12% over three years adds £1.1m of incremental net revenue relative to a flat-rate scenario at Year 3 — the equivalent of £9m of additional GMV at the Year 3 rate. Take rate expansion is a highly leveraged value driver and should be explicitly explained to investors who may otherwise model a fixed rate.
Explaining the Model to SaaS-Familiar Investors
Most UK growth-stage investors are more familiar with SaaS metrics than marketplace metrics. The translation requires three key clarifications.
First, GMV is not ARR. ARR is contracted, recurring, and recognised as revenue. GMV is facilitated transaction volume, and only the take rate component is the marketplace's revenue. Present your net revenue figure prominently and do not allow GMV to be confused with revenue in the first conversation.
Second, marketplace gross margins are naturally lower than SaaS gross margins because of payment processing costs (which flow through COGS for most marketplace structures). A SaaS business with 80% gross margin is not comparable to a marketplace with 65% gross margin; the marketplace's gross margin should be assessed in the context of the take rate, because the effective margin on the gross transaction is (take rate × gross margin), which for a 12% take rate and 70% gross margin is 8.4% of GMV. This is the correct basis for comparing marketplace economics across categories.
Third, the CAC for both sides of the marketplace must be disclosed. Many marketplace founders present only buyer CAC. Investors should ask for seller CAC as well, and the LTV calculation should explicitly address both sides. A marketplace that is economically efficient on the buyer side but is subsidising sellers heavily will have a structurally different long-term P&L than one that is balanced on both sides.
Key Takeaways
- GMV is not revenue. Revenue is GMV multiplied by the take rate. Conflating the two is the most common financial modelling error in marketplace companies.
- Gross margin in a marketplace should be 60 to 80% or higher for a software-enabled marketplace. Gross margin below 50% on net revenue typically indicates either excessive payment costs or excessive variable support costs that require investigation.
- The contribution margin inflection point (gross profit exceeding variable acquisition cost per cohort) is the key milestone before scaling investment in the business.
- Buyer LTV and seller LTV must both be modelled. Seller unit economics are the more commonly neglected of the two, and seller retention is the most significant single predictor of long-term marketplace health.
- Take rate is a strategic variable, not a fixed assumption. Document the drivers of take rate expansion and compression explicitly in the financial model.
- When presenting to SaaS-familiar investors, the three key clarifications are: GMV is not ARR; marketplace gross margins are naturally lower; and CAC must be presented for both sides of the marketplace.
