The three MACRS conventions, and how to tell which one a schedule used

The convention is the narrowest column on a depreciation schedule. Two letters, sometimes buried inside a method string, often not printed at all.

It also moves the first-year number more than anything else on the row. The same asset, the same cost, the same recovery period and the same method can produce a first-year deduction seven times larger under one convention than under another. Nothing else on the line has that range.

There are three, and which one governs is not a preference. Each follows from facts — what kind of property it is, and when during the year the client's assets were placed in service — and one of those facts is about the whole year rather than about the asset in front of you. That last point is what makes a missing convention column a genuine problem rather than an inconvenience.

The half-year convention, and what default means here

Under the half year convention, property is treated as placed in service at the midpoint of the tax year, whatever the actual date. Half a year of depreciation in the first year, and the recovery spills one year past the nominal class life to pick up the other half at the end — which is why five-year property sits on a schedule for six years.

It applies to personal property, which is to say everything that is not residential rental or nonresidential real property, and it is what governs unless the mid-quarter test below is tripped.

Calling it the default is accurate but slightly misleading. Nobody elects it. It applies because the alternative did not.

The mid-quarter convention, and the 40% test that triggers it

The mid quarter convention treats property as placed in service at the midpoint of the quarter in which it was actually placed in service. Four possible first-year fractions instead of one.

It is triggered by a test on the whole year: if the aggregate basis of MACRS property placed in service during the last three months of the tax year exceeds 40% of the aggregate basis of all MACRS property placed in service during the entire year, mid-quarter applies. Residential rental and nonresidential real property are excluded from both sides of that computation, since they run on mid-month regardless.

Two consequences are worth being explicit about, because they are where the reasoning usually goes wrong.

It is all-or-nothing for the year. If the test is tripped, every item of personal property placed in service that year moves to mid-quarter — not only the ones bought in the fourth quarter. An asset acquired in February is affected by a purchase made in December.

It is a fact about the client's year, not about the asset. Nothing on an individual row can tell you whether the test was met. The row does not know what else was bought.

The mid-month convention, and why real property is separate

The mid month convention treats property as placed in service at the midpoint of the month, and it applies to residential rental property and to nonresidential real property. Twelve possible first-year fractions.

The arithmetic is simple enough to state in one line: the first year takes (12 − month + 0.5) ÷ 12 of a full year's straight-line depreciation. Property placed in service in January gets 11.5 months of the twelve; property placed in service in December gets half a month.

For 27.5-year residential rental property that works out to 3.485% of basis in a January year and 0.152% in a December one. The full grid for every month and both real property classes is in Publication 946, Appendix A, and is worth reading there rather than from a copy.

Real property is on straight line throughout, so unlike the other two conventions there is no interaction with a declining-balance rate to reason about.

Reading the convention off the numbers

This is the useful part when a schedule arrives from a prior preparer with no convention column, which happens often.

The convention is visible in the first-year deduction as a fraction of basis, because each convention produces a distinct first-year percentage for a given class and method. For the declining-balance classes those percentages are exact and easy to recognise:

First-year rate	3-year 200DB	5-year 200DB
Half-year	33.33%	20.00%
Mid-quarter, Q1	58.33%	35.00%
Mid-quarter, Q2	41.67%	25.00%
Mid-quarter, Q3	25.00%	15.00%
Mid-quarter, Q4	8.33%	5.00%

They are not arbitrary. The annual declining-balance rate is 2 ÷ life, and the convention decides what fraction of the year it runs for — six months out of twelve under half-year, and 10.5, 7.5, 4.5 or 1.5 months under mid-quarter by quarter. For five-year property the annual rate is 40%, so half-year gives 20.00% and a fourth-quarter acquisition gives 5.00%. The same construction works for any class and any declining-balance rate.

So: take a row whose first year is on the schedule, divide the first year's depreciation by the basis, and compare. A five-year row showing 5% of cost in its first year was placed in service in a fourth quarter under mid-quarter. One showing 20% was under half-year.

Two cautions. The method has to be the one you assume — a 150% declining-balance row has different percentages, derived the same way from 1.5 ÷ life. And this identifies what the prior preparer's software did, which is the fact you need in order to transcribe the schedule faithfully. It is not a view about what should have been done, and it cannot be, because the 40% test depends on the year's full acquisition list and that list is not on the page.

Where the schedule shows only later years, this does not work at all: from year two onward the half-year and mid-quarter percentage series diverge in ways that are not distinctive enough to read by eye.

The other route is the return. Column (e) of Part III, Section B of Form 4562 states the convention for that year's additions, one row per property class.

The disposal year, where the convention returns

A convention applies at both ends. It governs the year an asset leaves as well as the year it arrives.

Under half-year, a disposal takes half a year's depreciation in the year of sale regardless of the date. Under mid-quarter, it takes depreciation to the midpoint of the quarter of disposal. Under mid-month, to the midpoint of the month.

This is the part most often missed when an asset base is rebuilt in new software, because the convention field is treated as first-year metadata and quietly dropped once the asset is a few years old. It stops being relevant right up until the client sells something.

What we do with it

The convention is transcribed from what the schedule prints. Where it is printed in its own column, or inside a compressed method string such as 5 HY 200DB, it is read from there.

Where it is not printed at all, the field comes back empty and flagged rather than filled with the convention that is most likely. Half-year is the most likely, and writing it in would be right most of the time — which is exactly why it is not done. A convention silently supplied by us, wrong in the minority of cases where the client had a heavy fourth quarter, would be indistinguishable on the page from one the document actually stated.

Before any of that, the extracted rows are checked against the schedule's own printed subtotals and grand total. A convention has no effect on that check, since it is not a dollar amount — which is another reason it is left to the preparer rather than inferred.

If the convention is missing and matters, the cleanest route is to ask for the detailed print or the fixed-asset export, the same as with any other absent column. What a schedule carries and what it drops is covered in reading a MACRS depreciation schedule, and the wider question of what survives a software change is on the switching tax software page.

FAQ

What are the three MACRS conventions?

Half-year, mid-quarter and mid-month, printed as HY, MQ and MM. Half-year and mid-quarter apply to personal property; mid-month applies to residential rental and nonresidential real property.

What triggers the mid-quarter convention?

The aggregate basis of MACRS property placed in service during the last three months of the tax year exceeding 40% of the aggregate basis of all MACRS property placed in service during the whole year, with residential rental and nonresidential real property excluded from the computation. When the test is met, every item of personal property placed in service that year uses mid-quarter, not only the fourth-quarter acquisitions.

What is the half-year convention?

Treating property as placed in service at the midpoint of the tax year regardless of the actual date, so the first year takes half of a full year's depreciation and the recovery extends one year beyond the nominal class life.

Which property uses the mid-month convention?

Residential rental property and nonresidential real property. The first year takes (12 − month + 0.5) ÷ 12 of a full year's straight-line depreciation, so a January in-service date gets 11.5 months of the twelve and a December one gets half a month.

Can I work out the convention from a schedule that does not print it?

From a first-year row, yes. Divide the first year's depreciation by the basis and compare against the first-year percentages for that class and method — five-year 200DB gives 20.00% under half-year and 35.00%, 25.00%, 15.00% or 5.00% under mid-quarter by quarter. From a later year it is not reliably readable. That year's Form 4562, column (e) of Part III Section B, states it directly.

Does the convention matter after the first year?

Yes, at disposal. The convention governs how much depreciation the year of sale takes — half a year under half-year, to the midpoint of the quarter under mid-quarter, to the midpoint of the month under mid-month. It is easy to treat as first-year metadata and drop, and the omission surfaces only when something is sold.