Straight-Line vs Sum-of-Years-Digits Depreciation in Google Sheets

August 7th, 2026

Depreciation spreads an asset's cost over its useful life. Two common methods land in everyday spreadsheet models: straight-line (same expense every period) and sum-of-years-digits (front-loaded expense). Google Sheets implements them as SLN and SYD, with DB and DDB nearby for declining-balance variants. This guide compares SLN and SYD with year-by-year formulas you can paste into a sheet.

The three inputs every method shares

| Input | Meaning | | --- | --- | | Cost | What you paid (capitalized basis) | | Salvage | Expected value at end of useful life | | Life | Number of periods (usually years) |

Depreciable base = cost − salvage. Methods differ only in how fast that base is recognized as expense.

SLN — straight-line (constant each year)

SLN divides the depreciable base evenly across life:

=SLN(cost, salvage, life)

Example: machine costs $10,000, salvage $2,000, life 5 years:

=SLN(10000, 2000, 5)

Returns 1600 every year. Over five years: (5 × 1600 = 8000 = 10000 − 2000). Book value falls in equal steps: 10000 → 8400 → 6800 → 5200 → 3600 → 2000.

SYD — sum-of-years-digits (higher early, lower late)

SYD weights early periods more. For life (n), the denominator is (1+2+\cdots+n = n(n+1)/2). Year (k) uses remaining life weight ((n−k+1)):

=SYD(cost, salvage, life, period)

Same asset, year by year:

=SYD(10000, 2000, 5, 1)
=SYD(10000, 2000, 5, 2)
=SYD(10000, 2000, 5, 3)
=SYD(10000, 2000, 5, 4)
=SYD(10000, 2000, 5, 5)

With sum-of-years = 15, depreciable base 8000:

| Year | Weight | SYD expense | | --- | --- | --- | | 1 | 5/15 | ~2,666.67 | | 2 | 4/15 | ~2,133.33 | | 3 | 3/15 | 1,600.00 | | 4 | 2/15 | ~1,066.67 | | 5 | 1/15 | ~533.33 |

Total still 8,000. Expense starts above straight-line and finishes below it.

Year-by-year comparison table (formulas)

Layout:

| Cell | Content | | --- | --- | | B1 | Cost 10000 | | B2 | Salvage 2000 | | B3 | Life 5 | | A6:A10 | Periods 1 … 5 |

=SLN($B$1, $B$2, $B$3)
=SYD($B$1, $B$2, $B$3, A6)

Put SLN in a column and fill the same value down (it does not depend on period). Put SYD next to each period number in A. Optional cumulative expense:

=SUM($C$6:C6)

for SLN amounts in column C, and the same pattern for SYD in column D. Ending book value after year k:

=$B$1 - SUM($D$6:D6)

Both methods should reach salvage after the final period (within rounding).

Side-by-side intuition

| | Straight-line (SLN) | Sum-of-years-digits (SYD) | | --- | --- | --- | | Pattern | Flat | Front-loaded | | Best when | Benefit is even over time | Asset loses usefulness faster early | | Args | cost, salvage, life | cost, salvage, life, period | | Period needed? | No | Yes |

In year 1 of the example, SYD expenses about 2,667 vs SLN 1,600 — more cost recognized while the asset is newest. By year 5 the relationship flips.

Declining balance in brief: DB and DDB

When you need classic declining-balance schedules:

• DB — fixed-declining balance using a rate derived from cost, salvage, and life (supports a month argument for partial first year).
• DDB — double-declining balance (or another factor you pass); does not automatically stop at salvage the same way SLN/SYD do, so models often cap the last period.

=DDB(10000, 2000, 5, 1)
=DB(10000, 2000, 5, 1)

Use SLN/SYD when policy or teaching examples call for those methods; use DB/DDB when the books follow declining-balance rules.

Common mistakes

• Forgetting period on SYD. =SYD(10000, 2000, 5) is incomplete; each year needs its period index.
• Period outside 1…life. =SYD(…, 6) on a 5-year life errors or misleads — keep period in range.
• Salvage ≥ cost. Depreciable base should be positive; zero base means zero depreciation.
• Mixing units of life. If life is in years, do not feed a month number as period unless life is also in months.
• Expecting SLN to change by year. Flat is the point; use SYD, DB, or DDB for acceleration.

Which method should you pick?

| Goal | Function | | --- | --- | | Even expense each period | SLN | | Accelerated, sum-of-years pattern | SYD | | Declining-balance style | DB / DDB |

Going further

Depreciation sits next to loans, NPV, and bonds in Sheets' finance set — see Mastering Financial Functions in Google Sheets. References: SLN, SYD, DB, DDB.