Strategic Cost Management · Activity Based Cost Management

Activity Based Budgeting and Time-Driven ABC Explained

Updated 11 October 2026 · Fact-checked

Activity based budgeting (ABB) builds the budget from the activities needed to meet planned output, then costs the resources those activities need. Time-Driven ABC (TDABC) costs activities using a capacity cost rate (cost per minute of capacity supplied) multiplied by the time each activity takes, from a time equation.

Understand Activity Based Budgeting and Time-Driven ABC

Traditional budgets start with last year's figures and add or cut a percentage. They show what you spend, not why. Activity based budgeting (ABB) reverses this. You first forecast the output and sales. Then you work out how many times each activity must be done. Then you work out the resources needed to do those activities, and cost them.

The logic is: output drives activity demand, and activity demand drives resource cost. For example, more orders means more purchase order processing, which needs more purchasing staff time. ABB also exposes unused capacity. If resources you have bought exceed what the budgeted activities need, you see the gap and can decide to cut it or use it.

Classic ABC assigns resource cost to activities using staff estimates of the percentage of time spent, then to products through cost drivers. It needs surveys and is costly to update. Time-Driven ABC (TDABC) simplifies this. It asks only two questions: how much does it cost per minute to supply capacity, and how many minutes does each transaction need?

The capacity cost rate is the cost of a resource department divided by the practical capacity of that resource in time units. Practical capacity is usually below theoretical capacity because of breaks, training and idle time. Each activity then gets a time equation: the standard time plus extra time for special features, such as urgent orders or foreign suppliers. Cost of an activity = capacity cost rate × time used.

Because TDABC uses practical capacity, cost charged to products covers only the time used. The cost of unused capacity is shown separately and not loaded onto products. This is a key difference from traditional ABC, which can spread the cost of idle capacity into product costs.

Key rules to remember

Activity demand: Activity volume = Budgeted output ÷ Output per unit of cost driver (or cost driver units per unit of output × budgeted output); Use the cost driver of each activity, for example orders, set-ups or inspections.
Activity based budget cost: Budgeted activity cost = Budgeted driver volume × Cost per driver unit; Total budget = sum of all activity budgets plus any unit-level costs.
Resource requirement: Resources needed = Activity demand ÷ Capacity per resource unit; Round up where resources are indivisible, such as people or machines, and state the assumption.
Capacity cost rate: Capacity cost rate = Cost of capacity supplied ÷ Practical capacity (in time units); Use the cost of the resource department. Practical capacity excludes breaks and unavoidable idle time.
Time equation: Time = β0 + β1X1 + β2X2 + ...; β0 is the standard time. Each X is a driver of extra time and β is the minutes per unit of that driver.
TDABC activity cost: Cost of activity = Capacity cost rate × Time per activity (from time equation); Total cost assigned = rate × total time used.
Cost of unused capacity: Unused capacity cost = Capacity cost rate × (Practical capacity − Time used); Equals cost of capacity supplied less cost assigned to activities.

How to solve Activity Based Budgeting and Time-Driven ABC questions

Use this order for any numerical on activity based budgeting or TDABC. Show each step so the marker can award method marks.

1Read the question and decide the task: an ABB budget, a TDABC cost rate, or a comparison with traditional costing.
2List the budgeted output or the number of transactions for each product or customer.
3For ABB: convert output into activity demand using each cost driver, then compute resource needs and cost.
4For TDABC: compute practical capacity in minutes (people × days × hours × 60, less stated breaks or idle time).
5Compute the capacity cost rate = departmental cost ÷ practical capacity in minutes.
6Build the time for each activity using the time equation, adding the extra minutes only where the feature applies.
7Multiply time by the rate, then total by product or customer. Compute unused capacity cost and check that assigned cost plus unused cost equals the resource cost.
8Write a short conclusion: the budget total, unit cost, unused capacity or the action management should take.

Quickest way: Rate, time, cost check

When to use it: Use for TDABC numericals where the department cost and practical capacity are clear.

Write the capacity cost rate first, per minute, to two or three decimals.
Convert every activity into minutes using the time equation before multiplying.
Total minutes used across all activities and compare with practical capacity.
Compute assigned cost = rate × minutes used, and unused cost = rate × idle minutes.
Confirm the two add up to the department cost. If not, find the slip before moving on.

Common mistakes in Activity Based Budgeting and Time-Driven ABC

Using theoretical capacity instead of practical capacity in the capacity cost rate.
Students take 8 hours × days without deducting breaks or idle time stated in the question.
Fix: Underline the practical capacity percentage or the deductions in the question and apply them before dividing.
Loading unused capacity cost onto products in TDABC.
Habit from traditional ABC where all resource cost is spread to cost drivers.
Fix: Charge only rate × time used to products. Show unused capacity cost as a separate line.
Forgetting to add the extra time in the time equation, or adding it for every unit.
The equation has several terms and students apply all of them to all transactions.
Fix: Add each extra term only for transactions that have that feature, for example urgent orders or new customers.
Mixing units, such as a rate per hour with time in minutes.
Capacity is given in hours and activity times in minutes.
Fix: Convert everything to minutes at the start and write the unit next to each number.
Preparing an ABB by simply adding a percentage to last year's budget.
Students carry over the incremental budgeting habit.
Fix: Start from budgeted output, derive activity volumes, then cost resources. State the cost driver for each activity.
Not rounding up resources that cannot be split.
Students stop at the division result, such as 4.3 staff.
Fix: If people or machines are indivisible, round up and show the resulting spare capacity, unless the question allows part-time use.

Worked examples

Example 1

Sundaram Auto Parts Ltd budgets 12,000 units of product P and 8,000 units of product Q. Each unit of P needs 1 inspection batch per 100 units; Q needs 1 batch per 50 units. Cost per inspection batch is ₹600. Set-ups: P needs 1 set-up per 500 units; Q needs 1 per 400 units. Cost per set-up is ₹2,500. Prepare an activity based budget for these two activities.

Show the solution

Inspection batches for P = 12,000 ÷ 100 = 120. For Q = 8,000 ÷ 50 = 160. Total = 280.
Inspection budget = 280 × ₹600 = ₹1,68,000. P = 120 × 600 = ₹72,000. Q = 160 × 600 = ₹96,000.
Set-ups for P = 12,000 ÷ 500 = 24. For Q = 8,000 ÷ 400 = 20. Total = 44.
Set-up budget = 44 × ₹2,500 = ₹1,10,000. P = 24 × 2,500 = ₹60,000. Q = 20 × 2,500 = ₹50,000.
Total for P = ₹72,000 + ₹60,000 = ₹1,32,000. Total for Q = ₹96,000 + ₹50,000 = ₹1,46,000.
Check: ₹1,32,000 + ₹1,46,000 = ₹2,78,000 = ₹1,68,000 + ₹1,10,000.

Answer: Budget: inspection ₹1,68,000 and set-up ₹1,10,000, total ₹2,78,000. Product P ₹1,32,000 and product Q ₹1,46,000. Per unit: P ₹11 and Q ₹18.25.

Example 2

The order processing department of Kaveri Traders has 10 staff. Monthly cost of the department is ₹4,80,000. Each person works 20 days a month, 8 hours a day, but practical capacity is 75% of this time. The time equation for processing a sales order is: 6 minutes + 4 minutes if the order is for export + 3 minutes if the customer is new. In a month there are 3,000 orders: 600 are export orders and 400 are for new customers. Calculate the capacity cost rate, the cost assigned to orders and the cost of unused capacity.

Show the solution

Theoretical capacity = 10 × 20 × 8 × 60 = 96,000 minutes.
Practical capacity = 75% × 96,000 = 72,000 minutes.
Capacity cost rate = ₹4,80,000 ÷ 72,000 = ₹6.667 per minute (₹20 per 3 minutes).
Standard time = 3,000 × 6 = 18,000 minutes.
Export extra = 600 × 4 = 2,400 minutes. New customer extra = 400 × 3 = 1,200 minutes.
Total time used = 18,000 + 2,400 + 1,200 = 21,600 minutes.
Cost assigned = 21,600 × 4,80,000 ÷ 72,000 = 21,600 × 6.6667 = ₹1,44,000.
Unused minutes = 72,000 − 21,600 = 50,400. Unused cost = 50,400 × 6.6667 = ₹3,36,000.
Check: ₹1,44,000 + ₹3,36,000 = ₹4,80,000.

Answer: Capacity cost rate is about ₹6.67 per minute. Cost assigned to orders is ₹1,44,000 (₹48 per order on average). Unused capacity cost is ₹3,36,000, so management should review staffing or find more work for the team.

Exam tips

Write the cost driver next to each activity in an ABB answer. Markers look for the driver-to-activity link.
In TDABC, always show practical capacity, the rate and the unused capacity cost. Many answers lose marks by skipping the last one.
When asked to compare ABC and TDABC, give three points: how time is estimated, treatment of idle capacity and ease of updating.
End numerical answers with one line of advice, such as reducing excess staff or repricing complex orders. This is a decision-oriented paper.
Keep the check total (assigned plus unused equals resource cost) at the bottom of your working to confirm accuracy.

Practice questions from Activity Based Cost Management

Activity Based Budgeting and Time-Driven ABC in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Activity Based Budgeting and Time-Driven ABC: frequently asked questions

What are the steps in activity based budgeting?

Forecast output and sales, identify the activities needed, choose a cost driver for each, compute activity volumes, work out the resources required and cost them. Then add unit-level costs and review for unused capacity. Compare the result with the previous budget to see where the cost changes.

What is the difference between ABC and TDABC?

Traditional ABC uses employee surveys to split resource cost across activities by percentage of time. TDABC uses a capacity cost rate and a time equation for each activity. TDABC is easier to update and shows unused capacity cost separately instead of loading it on products.

How do you calculate the capacity cost rate in TDABC?

Divide the cost of the resource department by its practical capacity in time units, usually minutes. Practical capacity is the time available after breaks and unavoidable idle time. For example, ₹4,80,000 divided by 72,000 minutes gives about ₹6.67 per minute.

What is a time equation in TDABC?

It is a formula giving the time an activity takes, starting from a standard time and adding extra minutes for features that complicate the work. For instance, an order may take 6 minutes plus 4 minutes if it is for export. It lets one equation cover many different transactions.