Indirect cost allocation assigns shared expenses - management salaries, IT, facilities, quality control - to products, clients, or services. The four main methods are single-rate volume-based allocation, departmental rates, Activity-Based Costing (ABC), and Time-Driven Activity-Based Costing (TDABC). Each produces different profitability results for the same business. Volume-based methods hide cost-to-serve differences between customers. TDABC, developed by Kaplan and Anderson, uses time equations to model actual resource consumption without employee surveys, making it scalable for complex operations with dozens of activity types.
What Are Indirect Costs, Exactly?
Indirect costs are expenses that cannot be directly traced to a single product, client, or service — things like management salaries, IT infrastructure, quality control, finance, HR, facilities. In most companies, these represent 30–60% of total costs.
The question is never whether to allocate them. The question is how.
The Four Main Methods (and What They Hide)
1. Single Rate / Volume-Based Allocation
The simplest approach: pick one driver (usually revenue, headcount, or direct labour hours) and spread everything proportionally.
What it hides: A client generating €500K in revenue but requiring 3x the customer service touchpoints looks identical to a client generating €500K with minimal service demand. One is profitable. The other probably isn’t.
2. Departmental Rates
A step up — each department gets its own allocation rate. Better, but still ignores how much of each department’s capacity each product or client actually consumes.
3. Activity-Based Costing (ABC)
Costs are assigned to activities first, then to cost objects based on actual consumption of those activities. A product that requires 12 quality checks is allocated 12x more quality cost than one that requires 1.
The limitation: ABC requires significant data infrastructure and regular maintenance to stay accurate.
4. Time-Driven Activity-Based Costing (TDABC)
An evolution of ABC developed by Kaplan and Anderson. Instead of surveying employees about time allocation (which produces biased data), TDABC uses time equations to estimate the capacity consumed by each transaction type.
TDABC is the method we use in CostCTRL because it scales — you can model a complex operation with dozens of activity types without the interview burden of traditional ABC.
The Real Cost of Choosing Wrong
A manufacturing client we worked with had been allocating overhead using revenue as the single driver for 11 years. When we rebuilt their model using TDABC, three of their seven product lines flipped from profitable to loss-making. The products they had been prioritising in sales were the ones destroying margin.
This is not unusual. In our diagnostic work, we see this pattern in roughly 40% of mid-market companies.
How to Choose the Right Method
The right method depends on your cost complexity and data maturity:
- High cost complexity + low data maturity → start with improved departmental rates, plan for TDABC
- High cost complexity + high data maturity → TDABC
- Low cost complexity → ABC or even volume-based rates may be sufficient
The worst outcome is using a method that’s more sophisticated than your data supports — you’ll produce precise numbers that are precisely wrong.
A Simple Diagnostic
Ask yourself: if your two largest clients both generate the same revenue, could you tell within 48 hours which one consumes more of your indirect capacity? If the answer is no, your allocation method is costing you money.
The Profitability Health Check includes a dedicated Cost Allocation dimension that assesses your current method against six criteria. It takes 4 minutes and gives you a benchmark against companies in your sector.