Short answer. By days, not by lump sums. The Civil Code treats civil fruits such as rent as accruing daily, and they belong to the usufructuary in proportion to how long the usufruct lasts. So rent is split according to the days each side was entitled during the period it covers.
What the law says
Civil fruits are deemed to accrue daily, and belong to the usufructuary in proportion to the time the usufruct may last.
Civil Code, Article 569 — Civil Fruits Accrue Daily. Read the full provision →
What civil fruits are, and why daily accrual matters
A usufruct lets one person enjoy property that belongs to another. Civil fruits are the income the property yields under a legal relationship — rent from a lease, the price of a right granted over the land, income from certain investments. Article 569 says these are deemed to accrue daily. That single word decides most disputes. Rent is not treated as earned on the day it happens to be collected, nor on the first day of the month, but bit by bit across the period it covers. A usufruct that ends mid-month therefore does not hand the whole month's rent to either side.
Working out the split
Take the rent for the period the payment covers, count the days in that period, and give the usufructuary the days during which the usufruct was still running. If a monthly rent is payable for a thirty-day month and the usufruct ended on the tenth, roughly a third belongs to the usufructuary or, if he has died, to his heirs, and the rest to the owner. The same arithmetic works at the start: a usufruct that begins mid-period gives the usufructuary only the days from its commencement. Timing of collection is irrelevant — rent already collected in advance may have to be shared back, and rent collected later still has to be traced to the days it covers.
How this differs from crops and other natural fruits
The daily rule is peculiar to civil fruits. Natural and industrial fruits — crops, harvests, the young of animals — are governed by different rules, which look at whether the fruits were hanging at the start of the usufruct and at whether they were pending when it ended, with an accounting for cultivation expenses. So a usufructuary of farmland and a usufructuary of an apartment building are not in the same position at all. It also helps to remember what a usufructuary is not. He is not the owner, cannot sell the property, and must preserve its form and substance and return it when the usufruct ends.
Practical points and where disputes start
Most fights arise where the usufruct ends on death and the tenant keeps paying the same person out of habit, or where the owner cancels the lease the moment the usufruct lapses. A few precautions help. Fix in writing who collects rent and where it is deposited; tell the tenant in writing when the entitlement changes, so payment goes to the right hands; keep the lease, the receipts and the deed or will that created the usufruct together. Remember too that the usufructuary generally bears ordinary maintenance and the charges on the fruits, so the gross rent is not the amount in dispute. This is general information on the article; for a specific accounting, book a consultation with the firm.