The half-year rule is the CRA convention that, in the year a capital asset is acquired, only half of its cost can be added to the class’s UCC for CCA purposes that year. The other half is held back and added to the UCC pool at year end, so it’s available for full-rate depreciation in the next year.
The rule exists to block a tax-gaming pattern. Without it, a corporation could buy a big-ticket asset on December 31 and claim a full year’s CCA on it for the year just ending, even though the asset was effectively held for one day. The asset could then be sold on January 1 with almost no tax consequence: buy in December, claim full CCA, sell in January, repeat. The half-year rule blunts this by averaging the depreciation across the acquisition year.
Mechanically:
- Reduced UCC (for CCA calculation purposes in year ):
- CCA claim for the year:
- Closing UCC, with the deferred half added back:
A worked example. Buy a $100,000 asset (Class 8, ) in year 1, no other transactions:
- UCC_{\text{reduced}}(1) = 0 + \tfrac{1}{2}(100{,}000) - 0 = \50{,}000$.
- CCA(1) = 50{,}000 \cdot 0.20 = \10{,}000. Only half of the "expected" \20,000.
- UCC_{\text{end}}(1) = 50{,}000 - 10{,}000 + 50{,}000 = \90{,}000$.
For year 2 (no transactions):
- UCC_{\text{reduced}}(2) = 90{,}000 + 0 - 0 = \90{,}000$.
- CCA(2) = 90{,}000 \cdot 0.20 = \18{,}000$.
- UCC_{\text{end}}(2) = 90{,}000 - 18{,}000 = \72{,}000$.
From year 2 onward, CCA proceeds at the full rate on the actual book value. Total CCA over the life of the asset is the same regardless of when you start; the half-year rule only delays it by about half a year.
The rule is baked into the standard derivation of the Capital tax factor (CTF), so when you use CTF in a PW analysis you’ve already accounted for it. Some asset classes and the Accelerated Investment Incentive modify or suspend the half-year rule, but for standard analysis it applies unless the problem says otherwise.