A tenant owes rent for this month, water from last month, and a balance carried from the month before. They send one amount that covers some but not all of it. Which charges did it pay?
That question has to have a rule, set once and applied every time. Without one the answer differs depending on who processes the receipt, and a balance stops being reproducible. Two people can look at the same account and disagree about what is owed, both honestly.
The common rules
Oldest charge first. Money clears the earliest outstanding item, then the next, until it runs out. The most widely used, and the easiest to explain to a tenant.
By charge type, in a stated priority. Rent before utilities, or utilities before rent because the supplier has to be paid either way.
As the payer instructed. Where a tenant states what a payment is for and that instruction is recorded, it generally governs, and this is the exception that has to be handled deliberately. A stated instruction that the system silently overrides is the one allocation error a tenant will be able to prove.
Any of these is defensible. What is not defensible is allocating differently in different months, because a balance produced by a consistent rule can be recalculated by anyone and reaches the same answer, while a balance produced case by case can only be defended by the person who made the judgements, for as long as they remember them.
A worked allocation
Tenant owes: August water KES 1,200, September rent KES 18,000, August arrears KES 4,300. Total KES 23,500.
They pay KES 20,000.
Under oldest-first, taking August items before September:
| Charge | Owed | Applied | Balance | | --- | --- | --- | --- | | August arrears | 4,300 | 4,300 | 0 | | August water | 1,200 | 1,200 | 0 | | September rent | 18,000 | 14,500 | 3,500 | | Total | 23,500 | 20,000 | 3,500 |
The receipt says exactly that. The tenant knows they are KES 3,500 short on September rent and clear on everything before it. The ageing report knows the remaining balance is 0 days old rather than 60.
Under a rent-first rule the same KES 20,000 produces a KES 3,500 balance aged 60 days instead. Same money, same tenant, different report. That is why the rule has to be stated rather than improvised.
Why it matters beyond tidiness
- Arrears can be aged, because every outstanding amount has a date.
- Disputes end quickly, because a receipt showing "3,000 to rent, 1,200 to water, 800 to arrears" answers the question before it is asked.
- The ledger balances, because nothing sits as an unapplied lump.
- Deposits stay out of it. A security deposit is not available to clear arrears mid-tenancy unless the agreement says so. It is not a payment on account.
What goes wrong
The most common failure is not a wrong rule. It is a receipt that records the money and never says what it cleared, which leaves the allocation in somebody's memory and takes it out of the record.
The second is silent reallocation. Somebody adjusts last month's allocation to make this month's report look better. The tenant's copy of the old receipt no longer matches the account, and the first person to notice will be the tenant. Corrections belong in new entries that reference the original, for the same reason they do in a double-entry ledger.