A machine is purchased for
₹5,00,000. Five years later, someone asks, “How much depreciation should be
charged every year?” The calculation looks simple—but one small mistake about
residual value or useful life can change the entire answer.
The Straight Line Method becomes
easy once you stop treating it as a formula to memorise and instead see what
the formula is actually doing: spreading the depreciable cost of an asset
evenly over its useful life.
So, how do you calculate depreciation correctly? Start with the three figures that control the calculation.
What
is Straight Line Method of Depreciation?
The Straight Line Method is a
depreciation method in which the depreciable amount of an asset is charged as
an equal amount of depreciation over its estimated useful life. The annual
depreciation remains constant when the asset has a fixed cost, residual value,
and useful life.
The basic calculation considers the cost
of the asset, residual value, and useful life.
Straight
Line Method Explained Simply
Think of depreciation as the portion
of an asset's cost that is allocated to the accounting periods benefiting from
its use.
Suppose a business purchases a
machine for ₹5,00,000 and expects to use it for 5 years. If the machine is
expected to have a residual value of ₹50,000 at the end of those five years,
the entire ₹5,00,000 is not depreciated.
Why?
Because the business expects to
recover ₹50,000 when the machine is disposed of. Therefore, only ₹4,50,000 is
the depreciable amount.
That ₹4,50,000 is then spread
equally over five years:
₹4,50,000 ÷ 5 = ₹90,000 per year.
This is the central logic behind the
Straight Line Method.
Why
is depreciation equal every year?
Because the method assumes that the
depreciable amount should be allocated evenly over the asset's useful life. If
the underlying assumptions do not change, the same depreciation amount is
charged each year.
For example:
|
Year |
Depreciation |
|
Year 1 |
₹90,000 |
|
Year 2 |
₹90,000 |
|
Year 3 |
₹90,000 |
|
Year 4 |
₹90,000 |
|
Year 5 |
₹90,000 |
Notice something important: the
depreciation expense stays constant, but the book value of the asset decreases
every year.
The calculation therefore has two
different ideas:
- Depreciation expense
→ usually remains constant under SLM.
- Book value
→ decreases each year.
Beginners sometimes confuse these
two.
A professional, however, also asks
whether the estimated useful life and residual value remain reasonable. The
calculation is not simply about dividing a number; the assumptions behind that
number matter.
What
happens if there is no residual value?
If the asset has no estimated
residual value, the entire cost is depreciable.
For example, if an asset costs
₹2,00,000 and has a useful life of 5 years with nil residual value:
₹2,00,000 ÷ 5 = ₹40,000 annual
depreciation.
This is why identifying the residual
value before calculating depreciation is such a useful habit.
Straight
Line Method Formula
The basic formula is:
Annual Depreciation = (Cost of Asset
− Residual Value) ÷ Useful Life
Where:
- Cost of Asset
= purchase price plus directly attributable costs necessary to bring the
asset to its intended use, where applicable.
- Residual Value
= estimated amount expected to be recovered at the end of the asset's
useful life.
- Useful Life
= estimated period for which the asset is expected to be available for
use.
Another useful expression is:
Depreciable Amount = Cost of Asset −
Residual Value
Then:
Annual Depreciation = Depreciable
Amount ÷ Useful Life
If depreciation is required for only
part of a year, the annual depreciation may need to be apportioned according to
the applicable accounting or tax rules and the facts of the question.
Straight
Line Method Solved Example — Straightforward Case
Example
ABC Traders purchased a machine on 1
April 2026 for ₹6,00,000.
Additional installation cost was ₹50,000.
The estimated residual value of the
machine is ₹50,000, and its useful life is 5 years.
Calculate annual depreciation using
the Straight Line Method.
Step
1: Calculate the total cost of the asset
Purchase cost = ₹6,00,000
Installation cost = ₹50,000
Therefore:
Cost of asset = ₹6,00,000 + ₹50,000
= ₹6,50,000
The installation cost is included
because it is directly connected with bringing the machine into a condition
where it can be used.
Step
2: Deduct residual value
Cost of asset = ₹6,50,000
Less: Residual value = ₹50,000
Depreciable amount = ₹6,00,000
Step
3: Divide by useful life
Useful life = 5 years
Therefore:
Annual depreciation = ₹6,00,000 ÷ 5
Annual depreciation = ₹1,20,000
Step
4: Understand the result
ABC Traders will have annual
depreciation of ₹1,20,000 under the Straight Line Method, assuming the
stated estimates remain applicable.
The asset's carrying amount would
reduce as follows:
|
Year |
Opening
Book Value |
Depreciation |
Closing
Book Value |
|
1 |
₹6,50,000 |
₹1,20,000 |
₹5,30,000 |
|
2 |
₹5,30,000 |
₹1,20,000 |
₹4,10,000 |
|
3 |
₹4,10,000 |
₹1,20,000 |
₹2,90,000 |
|
4 |
₹2,90,000 |
₹1,20,000 |
₹1,70,000 |
|
5 |
₹1,70,000 |
₹1,20,000 |
₹50,000 |
At the end of five years, the book
value reaches the estimated residual value of ₹50,000.
That final check is worth doing. If
your calculation does not arrive at the expected residual value, revisit the
figures.
Common
Mistakes to Avoid
Wrong:
“Depreciation is always calculated on the original purchase price.”
Right: Under the Straight Line Method, depreciation is generally
calculated using the depreciable amount, which is cost less residual
value.
This mistake can cost marks because
students often immediately divide the purchase price by useful life without
checking whether a residual value has been provided.
Wrong:
“If annual depreciation is constant, the asset's book value also stays
constant.”
Right: Annual depreciation remains constant under the Straight
Line Method, but the asset's carrying amount decreases every year.
For example, if annual depreciation
is ₹1,20,000, the expense stays ₹1,20,000 each year, while the book value keeps
falling.
How
to Think About Straight Line Method in Real Life
Imagine an Indian manufacturing
business purchases a machine for ₹10 lakh. The accountant needs to decide how
much depreciation should be recognised each year.
The first question should not be,
“Which number should I divide?”
Instead, think in this order:
1. What is the asset's total cost?
Include relevant costs required to
bring the asset to the location and condition necessary for use.
2. Will anything be recovered at the
end?
If there is an estimated residual
value, do not depreciate that portion.
3. How long will the asset be
useful?
Determine the appropriate useful
life based on the applicable accounting framework and facts.
4. How much depreciable amount must
be allocated?
Subtract residual value from cost.
5. Does the result make sense?
Multiply annual depreciation by the
useful life and check whether the total equals the depreciable amount.
This last check is a small
professional habit that prevents surprisingly many calculation errors.
A student may stop after getting the
answer. An accountant usually checks whether the answer makes sense in relation
to the asset's expected closing value.
Exam
Tip
When an exam question gives cost,
residual value, and useful life, immediately write:
Depreciable Amount = Cost − Residual
Value
Then:
Depreciation = Depreciable Amount ÷
Useful Life
Do not divide the full cost by
useful life before checking for residual value. If the asset was purchased or
put to use partway through the year, also read the question carefully for the
required time apportionment.
Quick
Recap
- Straight Line Method charges an equal depreciation
amount over the useful life.
- The basic formula is (Cost − Residual Value) ÷
Useful Life.
- Depreciable amount means cost less estimated residual
value.
- Annual depreciation remains constant when the relevant
assumptions remain unchanged.
- Book value decreases every year even though annual
depreciation stays the same.
- Directly attributable costs may form part of the
asset's cost where applicable.
- Always check whether residual value has been given.
- For part-year use, consider the applicable
time-apportionment requirement.
Frequently
Asked Questions
Q: How do you calculate depreciation
using the Straight Line Method?
A: Subtract the estimated residual value from the asset's cost to find
the depreciable amount. Then divide that amount by the asset's useful life. The
resulting figure represents the annual depreciation when the asset is
depreciated evenly over its useful life.
Q: What is the formula for Straight
Line Method depreciation?
A: The formula is Annual Depreciation = (Cost of Asset − Residual
Value) ÷ Useful Life. If residual value is nil, the calculation becomes
cost divided by useful life. The applicable accounting framework should be
considered for the underlying assumptions.
Q: Why is depreciation the same
every year under SLM?
A: Straight Line Method allocates the depreciable amount equally across
the asset's useful life. Therefore, when cost, residual value, useful life, and
other relevant assumptions remain unchanged, the annual depreciation expense
remains constant.
Q: How do you calculate depreciation
if residual value is zero?
A: If the residual value is zero, the full depreciable cost is allocated
over the useful life. For example, an asset costing ₹3,00,000 with a five-year
useful life would have annual depreciation of ₹60,000 under the Straight Line
Method.
Q: Is book value the same as
depreciation expense?
A: No. Depreciation expense is the amount recognised for the period.
Book value is the asset's remaining carrying amount after accumulated
depreciation and other applicable adjustments. Under SLM, depreciation may
remain constant while book value decreases each year.
Related
Terms
→ Depreciation
→ Written Down Value Method
→ Accumulated Depreciation
→ Residual Value
→ Useful Life
Related
Guides
→ How does the Written Down Value
Method calculate depreciation, and when is it different from the Straight Line
Method?
The real skill in depreciation is
not memorising the SLM formula—it is knowing which amount belongs inside the
formula and why.
Hi, I'm Manoj Kumar — MBA, with
hands-on experience in accounting, taxation, and business concepts. Most
students don't struggle with commerce itself; they struggle because no one
breaks it down properly. That's what I focus on with Learn with Manika: simple,
logical steps that make concepts stick, whether you're prepping for exams or
just want to understand how things actually work.
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