How to Calculate Double Declining Balance Depreciation

To calculate double declining balance depreciation, take the straight-line rate for the asset’s useful life, double it, and apply that rate to the asset’s book value at the start of each year. The book value shrinks each year as depreciation accumulates, so the deduction gets smaller over time. At some point the formula stops working on its own and you switch to straight-line depreciation to finish writing the asset off. For federal tax purposes, a half-year convention and an assumed salvage value of zero also apply.

The mechanics are straightforward once you have the three inputs and know when the switchover happens.

What You Need Before You Start

Three numbers drive every calculation: cost basis, useful life, and salvage value.

Cost basis is more than the purchase price. It includes freight, installation, sales tax, and testing costs — every expense needed to get the asset ready for use.¹ A $95,000 machine with $3,000 in shipping and $2,000 in installation has a depreciable basis of $100,000.

Useful life depends on which set of books you’re working in. For federal tax purposes, you don’t estimate it yourself. The IRS assigns standardized recovery periods through the Modified Accelerated Cost Recovery System (MACRS): office machinery falls into the 5-year class, office furniture into the 7-year class, certain equipment into the 10-year class.² For book accounting under GAAP, your company estimates the life it actually expects to use the asset.

Salvage value is where tax and book depreciation split. Under GAAP, you estimate what the asset will be worth at the end and stop depreciating once book value reaches that floor. Under MACRS, salvage value is always treated as zero, so you depreciate the full basis.

Finding the Rate

Divide 1 by the number of years in the recovery period to get the straight-line rate, then double it. A 5-year asset has a straight-line rate of 20%, so the double declining rate is 40%. A 10-year asset moves from 10% to 20%. The IRS frames the shortcut as 2 divided by the recovery period.²

The rates for the MACRS classes that use the 200% declining balance method:

3-year property: 66.67% (2 ÷ 3)
5-year property: 40.0% (2 ÷ 5)
7-year property: 28.57% (2 ÷ 7)
10-year property: 20.0% (2 ÷ 10)

The rate doesn’t change from year to year. What changes is the balance you apply it to.

Year-by-Year Calculation

Multiply the beginning book value by the rate. Subtract that from book value. Repeat with the new balance next year. Using a $100,000 machine classified as 5-year property at 40%, and setting aside the half-year convention for now to show the pure math:

Year 1: $100,000 × 40% = $40,000 depreciation. Ending book value: $60,000.
Year 2: $60,000 × 40% = $24,000 depreciation. Ending book value: $36,000.
Year 3: $36,000 × 40% = $14,400 depreciation. Ending book value: $21,600.
Year 4: $21,600 × 40% = $8,640 depreciation. Ending book value: $12,960.
Year 5: $12,960 × 40% = $5,184 depreciation. Ending book value: $7,776.

After five years you’ve depreciated only $92,224 of a $100,000 asset. The remaining $7,776 never gets captured if you keep running the formula. That’s why every double declining balance schedule has to switch methods at some point.

Switching to Straight-Line

Left alone, the double declining formula never fully depreciates the asset. The fix is to switch to straight-line in the first year that straight-line produces an equal or larger deduction.² At the switchover, take the remaining book value, divide by the remaining years, and use that flat amount for each year that’s left.

Under MACRS the IRS has already worked out where the switch falls for each class:²

3-year property: switch in year 3
5-year property: switch in year 4
7-year property: switch in year 5
10-year property: switch in year 7

Going back to the $100,000 machine: in year 4, the declining balance formula gives $8,640. Straight-lining the $21,600 remaining balance over the 2 years left gives $10,800. Straight-line wins, so you switch. This is where hand-built spreadsheets most often go wrong. They either keep the declining balance formula running past the crossover point or forget to switch entirely, and undepreciated cost gets stranded on the books.

The Half-Year Convention

For federal tax purposes under MACRS, first-year depreciation is cut in half. Every asset placed in service during the year is treated as if you acquired it at the midpoint of the year, no matter when you actually bought it. You pick up the missing half at the end of the schedule in a partial final year.²

On the $100,000 machine at 40%, first-year MACRS depreciation is $20,000, not $40,000. The asset then runs over six calendar years instead of five, with a partial amount in year six. IRS Publication 946 provides percentage tables that already bake in both the half-year convention and the straight-line switch, so you can multiply the original basis by the year’s table percentage and skip the running-balance math entirely. Most tax software pulls directly from those tables.

One important exception: if more than 40% of the depreciable property you place in service during the tax year comes online in the last three months, you have to use the mid-quarter convention instead. Under that rule, each asset is treated as placed in service at the midpoint of the quarter it was actually acquired, which can meaningfully reduce first-year deductions on late-year purchases.

How the Final Years Work: MACRS vs. GAAP

The last few years of the schedule depend on which set of books you’re calculating for.

MACRS (Federal Tax)

Salvage value is zero. You depreciate the entire basis, and the IRS percentage tables handle the switchover and the conventions automatically. If you use the tables, the final-year percentage brings book value to exactly zero with no manual adjustment.²

Book Depreciation (GAAP)

You cannot depreciate below the estimated salvage value. As book value approaches that floor, you’ll hit a year where the formula would push it below salvage. In that year, record whatever amount brings book value down to salvage and stop. If your machine has a beginning book value of $8,000 and a salvage value of $7,500, the final entry is $500. That’s a manual plug figure that overrides the formula.

Tax and book schedules will almost always produce different numbers for the same asset. Tracking both is routine for corporate accounting, but smaller businesses sometimes lose track of which schedule feeds which report.

Which Assets Can Use This Method

The 200% declining balance method under MACRS applies to nonfarm 3-, 5-, 7-, and 10-year personal property placed in service under the General Depreciation System. Farm property in those classes qualifies if placed in service after 2017.²

Several categories cannot:

Land is never depreciable, because it doesn’t wear out or become obsolete.
Residential rental property must use straight-line over 27.5 years.
Nonresidential real property must use straight-line over 39 years.
15- and 20-year property uses the 150% declining balance method, not 200%.

If you’re unsure which class an asset falls into, Publication 946 contains detailed tables organized by asset type and industry.² Classification errors cascade through every year of the schedule, so it’s worth confirming at the outset rather than fixing later.

1
Internal Revenue Service. Publication 551 (12/2025), Basis of Assets
2
Internal Revenue Service. Publication 946 (2024), How To Depreciate Property