Financial Glossary
Marginal Cost
Marginal cost is the incremental cost incurred by producing and delivering one additional unit of output, holding all other factors constant. It is derived from total variable costs: as production scales, marginal cost equals the change in total cost divided by the change in quantity produced. In many businesses, marginal cost initially declines as fixed costs are spread and production efficiencies kick in (economies of scale), then eventually rises as capacity constraints force higher-cost production methods. Comparing marginal cost to marginal revenue determines whether expanding output increases or decreases profit: profit is maximized where the two are equal.
Problem & Application
A SaaS platform adds a new campground client to its reservation system. The marginal cost of adding this client includes incremental server compute, customer onboarding hours (say two hours of staff time at $60 per hour, or $120), and allocated support capacity. If infrastructure marginal cost is $30 per month for the additional load, total first-month marginal cost is $150, declining to $30 per month in subsequent months once onboarding is complete. The client pays $149 per month. After month one, marginal revenue exceeds marginal cost by $119 per month, making each additional client highly profitable at the margin. However, if the platform approaches server capacity limits and must provision a new tier of infrastructure costing $2,000 per month to add the next 20 clients, the marginal cost of that tranche of clients is $100 each per month before any onboarding expense, materially changing the unit economics calculation for that batch.
In Short
Marginal cost is an essential metric for cost management, helping businesses make informed decisions about production and pricing.