The straight line method spreads the cost of an asset evenly across every year of its life. The formula is short:
Annual depreciation = (Cost of the asset − Residual value) ÷ Useful life in years
Take an example. Buy a chiller for ₹3,40,000, expect ₹17,000 back at the end, and give it fifteen years of life. You charge ₹21,533 to the profit and loss account every year for fifteen years, and the figure never moves.
That flat charge is the whole appeal. It is also the method’s limit, because an asset that loses most of its value in year one is not wearing evenly, and a flat charge will overstate what it is worth. This guide covers the formula, its three inputs, and three worked examples.
Key Takeaways
- The formula is cost minus residual value, divided by useful life in years
- Schedule II sets useful life and caps residual value at 5% of cost
- An asset bought mid-year is charged pro rata, by days
- The charge is identical every year, so it is the easiest method to audit
- Your tax computation will not use these figures
What Is the Straight Line Method of Depreciation?
The straight line method, often shortened to SLM, writes off an equal amount of an asset’s cost in each year of its useful life. Plot the charge on a graph and it draws a flat line, which is where the name comes from.
It is not the only method available. ICAI teaching material lists straight line alongside reducing balance, sum of years digits and production units, and the accounting standards ask you to pick whichever matches how the asset’s benefits are consumed.
SLM is the default choice in most Indian books because it is simple to compute and simple to check. A reviewer who knows the cost, the residual value and the life can reproduce your figure in one line of arithmetic.
What Is the Straight Line Depreciation Formula?
Three inputs drive the whole calculation, and two of them are estimates rather than facts.
| Input in the SLM formula | Where the figure comes from | Common error |
|---|---|---|
| Cost of the asset | Purchase price plus everything spent to bring it into use, including freight and installation | Using the invoice value alone |
| Residual value | What you expect to recover at the end of the life, capped at 5% of cost | Assuming it is always zero |
| Useful life | Schedule II Part C for companies, or a justified estimate | Copying a tax rate instead |
Cost is the only one you can prove from a document. The other two are judgements, which is why two businesses holding the same machine can book different amounts against it and both be correct.
Where the Useful Life and Residual Value Come From
Schedule II of the Companies Act, 2013 gives a useful life in years rather than a rate. It states that useful life shall not ordinarily differ from Part C, and that residual value shall not be more than five per cent of original cost.
ICAI reads it the same way in its application guide on Schedule II, which also covers harder cases such as component accounting.
The full table of lives sits in our Schedule II depreciation chart, which works the rate out for fifteen asset classes under both methods.
3 Worked Examples of Straight Line Depreciation
Each example below is illustrative. The asset values are invented, but the useful lives come from Schedule II Part C, and the resulting rates match the published chart.
Example 1: A Full Year on a Display Chiller
A retail store buys a display chiller for ₹3,40,000 and puts it into use on 1 April, the first day of the financial year. It falls under plant and machinery, general, which carries a useful life of fifteen years.
Residual value at the 5% cap is ₹17,000. Deduct that from cost and the depreciable amount is ₹3,23,000.
₹3,23,000 ÷ 15 = ₹21,533 a year
Divide the annual charge by the original cost and you get 6.33%, which is the straight line rate Schedule II implies for a fifteen-year life. The figure repeats unchanged until the asset is fully depreciated down to its ₹17,000 residual.
Example 2: A Part Year on a Laptop Bought in November
Assets rarely arrive on 1 April. When one is bought partway through the year, the first year’s charge is worked out pro rata by days, and the same logic applies whichever of the depreciation methods you have chosen.
A garment wholesaler in Surat buys a billing laptop for ₹68,400 and puts it to use on 14 November. End user devices carry a useful life of three years under Schedule II.
Residual value is ₹3,420, so the depreciable amount is ₹64,980, and a full year would be ₹21,660. The asset was in use for 138 days of that financial year, from 14 November to 31 March, counting a non-leap February.
₹21,660 × 138 ÷ 365 = ₹8,189 in year one
Years two and three take the full ₹21,660, and the remaining ₹13,471 falls into a fourth part-year, because the three-year life started partway through year one.
Recording the date of purchase is what makes this possible, which is why it belongs in the fixed asset register rather than being reconstructed from an invoice in March.
Example 3: Restaurant Furniture on a Shorter Life
Schedule II gives some asset classes a shorter life in particular settings, and furniture is one of them.
General furniture and fittings run ten years. Furniture in hotels, restaurants and schools runs eight, on the reasoning that it takes heavier use.
A restaurant fits out its dining room for ₹2,85,000. Residual value is ₹14,250, leaving ₹2,70,750 to depreciate over eight years.
₹2,70,750 ÷ 8 = ₹33,844 a year
That works out to 11.88% of cost. Had the same furniture sat in a back office, the ten-year life would have produced ₹27,075 a year at 9.50%. The asset is identical. Only the setting changed the number.
The Same Chiller, First Six Years ₹60k ₹30k ₹0 Straight line Written down value Yr 1 Yr 2 Yr 3 Yr 4 Yr 5 Yr 6 Illustrative shapes on the Example 1 chiller. Straight line holds at ₹21,533; written down value starts higher and falls. Straight line holds the charge flat, while written down value front-loads it.When Does the Straight Line Method Fit?
SLM suits assets that give up their usefulness at a steady rate. A building, office furniture, a fit-out, a piece of plant running a constant shift pattern: all of these earn their keep evenly, so an even charge reflects what is happening.
It fits badly where an asset loses value fastest at the start. A vehicle is the standard case, and so is anything with rapid technical obsolescence, because a flat charge overstates the asset’s worth in the early years.
There is a second reason it stays popular. Because the number never changes, the charge is easy to budget and easy for a reviewer to reproduce, which matters more to a small finance team than theoretical accuracy.
Why Your Income Tax Return Will Not Show These Numbers
This catches people out at year end, so it is worth stating plainly. The figures you have just worked out are your book figures. Your tax computation runs on a different basis entirely.
Depreciation under the Income-tax Act works on a block of assets rather than asset by asset, and it uses the written down value method with rates from Appendix I to the Income-tax Rules, 1962.
So the laptop in Example 2 carries a straight line rate of 31.67% in your books and a different rate in the tax computation. Neither figure is wrong. The gap is a timing difference, which is why a fixed asset register normally carries both columns side by side.
How Does the Depreciation Charge Reach Your Accounts?
The annual figure is posted as a single entry: depreciation is debited, and accumulated depreciation is credited. Our journal entries guide shows the posting in full.
From there the charge appears as its own line in the profit and loss account, while the accumulated total sits against the asset on the balance sheet.
The two statements move together. It is also why depreciation is added back when working out EBITDA, since that measure deliberately strips it out.
All three inputs trace back to the original purchase. Across the records we see, the date an asset was put to use is the field most often missing, and it is the one the pro rata calculation cannot work without.
Petpooja Invoice keeps the supplier invoice, the date and the value against each purchase, so the cost and the date of use come from documents rather than from memory at year end.
Conclusion
The straight line method is the least complicated way to spread an asset’s cost, and for most assets on a small business balance sheet it is also the most honest one. Take the cost, take off a residual value of up to 5%, and divide by the useful life Schedule II gives you.
The arithmetic is the easy part. What tends to go wrong is the inputs: a cost that missed the installation charge, a purchase date nobody wrote down, or a life copied across from a tax rate.
Get those three right on the day you buy the asset and the depreciation looks after itself. Petpooja Invoice keeps that purchase trail intact so the register is built as you go.
Frequently Asked Questions
What is the straight line method formula?
Annual depreciation equals cost minus residual value, divided by useful life in years. The result is charged unchanged every year until the asset reaches its residual value. Dividing the annual charge by the original cost gives you the straight line rate as a percentage.
Is residual value always 5% under the straight line method?
No. Five per cent is a ceiling, not a default. Schedule II says residual value shall not be more than 5% of original cost, so you may use less where that reflects reality. Going above it means disclosing the difference and justifying it with technical advice.
How do you calculate straight line depreciation for a part year?
Work out the full-year charge first, then apportion it by the number of days the asset was in use. An asset put to use on 14 November runs 138 days to 31 March in a non-leap year, so the first-year charge is the annual figure multiplied by 138 and divided by 365.
Which is better, the straight line method or written down value?
Neither is better in the abstract. Straight line suits assets that wear evenly and keeps the charge predictable. Written down value suits assets that lose most value early. Both are permitted, and the total charged over the asset’s life is the same. What changes is the timing.
Can I use the straight line method for my income tax return?
Your tax computation follows the Income-tax Act, which works on blocks of assets and the written down value method, so your straight line figures stay in the books. A trial balance will confirm the book entry, but the tax number is worked out separately.
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Avani Joshi is a Content Writer at Petpooja, where she writes about payroll, billing, and the everyday software that keeps Indian SMEs running. She has a knack for taking complicated topics and explaining them in plain language for business owners who don't have time to decode jargon.
