A note on time-driven ABC: for advanced management accounting study

A note on time-driven ABC: for advanced management accounting study

 

Highlight 4 main ideas of time driven activity based costing in advanced management accounting study.

Four main ideas of TDABC

1.    Cost resources by practical capacity
TDABC begins by calculating a capacity cost rate: the cost of supplying a resource department divided by its practical working capacity, usually expressed as cost per minute. Practical capacity deliberately allows for breaks, training, meetings, and normal downtime.hbs+1

2.    Use time as the main cost driver
Instead of asking staff to estimate percentage effort across many activities, TDABC estimates the time needed for a transaction, service, product, or customer request. The basic calculation is:

Cost of activity = Time required × Capacity cost rate

This makes overhead assignment more closely related to actual resource consumption.

3.    Capture complexity with time equations
A time equation adjusts the basic processing time for features that make work more demanding—for example, an urgent order, a new customer, many line items, or a non-standard delivery. Thus, TDABC can model variation without creating an excessively large number of activity cost pools.hbr+1

4.    Make unused capacity visible for management
Because resource capacity supplied is compared with capacity actually used, TDABC identifies unused or idle capacity separately rather than forcing its cost into product or customer costs. Managers can then investigate excess capacity, inefficient processes, and potentially unprofitable customers or services.

A useful memory cue is: rate, time, variation, capacity.

Please provide a straightforward accounting example to illustrate the topic a bit more.

Simple TDABC example

Imagine a customer-service department whose annual operating cost is $240,000. Staff have 120,000 practical working minutes available during the year after allowing for breaks, meetings, and training.

1. Calculate the capacity cost rate

Capacity cost rate = Department cost / Practical capacity 

Capacity cost rate = $240,000 / 120,000 minutes = $2 per minute

 

So, every minute of customer-service time supplied costs the company $2. TDABC uses this rate rather than assigning all overhead through one broad percentage.

2. Cost two customer requests

A standard customer enquiry takes 5 minutes:

Cost of standard enquiry = 5 minutes×$2   

Cost of standard enquiry = $10

A complaint takes 5 minutes, plus 10 additional minutes for investigation:

Time for complaint = 5+10

Time for complaint = 15 minutes 

Cost of complaint = 15 minutes×$2

Cost of complaint = $30

The extra 10 minutes are a simple time equation: complex cases consume more resources and therefore receive more cost.

3. Identify unused capacity

Suppose the department actually uses 100,000 minutes during the year.

Used-capacity cost = 100,000×$2  

Used-capacity cost = $200

 Unused capacity = 120,000−100

Unused capacity = 20,000 minutes  

Cost of unused capacity = 20,000×$2

Cost of unused capacity = $40,000

Thus, TDABC reports $10 for a routine enquiry, $30 for a complaint, and separately highlights $40,000 of unused capacity—useful information for staffing and process-improvement decisions. This follows TDABC’s approach of assigning cost from a capacity cost rate and estimated activity time while keeping idle capacity visible.

Also study a related note on theoretical, practical and actual capacities.

** references:  a collection of management accounting notes; a useful generative AI tool.