Pro-rated first-month rent, with a worked example

A tenant's lease starts on the 14th of the month. They pay rent on the 1st. What do they owe on the 14th, and what do they owe on the 1st of the next month? It seems like trivial math, and it is, but the two common methods give different answers and the wrong one quietly costs you money on every move-in for years.

The two methods

Method A: actual days. Calculate the daily rate by dividing monthly rent by the actual number of days in that month, then multiply by the number of days the tenant occupies.

Method B: 30-day month. Calculate the daily rate by dividing monthly rent by 30, then multiply by the number of days the tenant occupies.

Both are widely used. The choice matters because the answers differ.

The math, side by side

Setup: monthly rent is $1,800, lease begins April 14, tenant occupies April 14–30 (17 days). April has 30 days.

Identical. So far so good. Now do February:

The actual-days method collects $64.29 more on a February move-in. Across a year of move-ins in months of varying lengths, the actual-days method generally collects slightly more in 28- and 30-day months and the same in 31-day months. The 30-day method is simpler arithmetically but is, on average, more favorable to the tenant.

When the lease starts late in the month

This is where the common mistake hides. If the lease starts late enough that pro-rating the first month leaves a small partial payment, many landlords skip the partial payment, charge the full first month at move-in, and treat the next 1st as the second month. Example: lease starts April 27, tenant pays $1,800 at move-in, the next 1st is May 1, and the landlord considers that May's rent.

What just happened: you collected $1,800 for four days of April plus all of May (35 days), at an effective daily rate of $51.43 instead of $60. You lost about $300 by being efficient.

The clean way: charge pro-rated rent at move-in for the days remaining in the partial month, then charge the first full month on the next 1st. In the example: charge $240 at move-in (4 days × $60), then $1,800 on May 1.

The reverse mistake

Some landlords pro-rate by collecting the full first month at move-in and then crediting the partial-month amount toward the second month. This is also common and not wrong, but it's confusing on the ledger and makes early lease-break accounting messier. Charge the partial month upfront. Charge the full months on schedule. Keep the line items clean.

What to write in the lease

Specify the pro-ration method explicitly. A clause like:

The first month's rent shall be pro-rated based on the actual number of days from the lease commencement date through the last day of that calendar month, calculated as the monthly rent divided by the number of days in that month, multiplied by the number of days of occupancy in that month.

Without this, a tenant who paid full rent for a partial month can later demand a refund using a different pro-ration formula and have a defensible claim.

Pro-rating at move-out

The same logic applies in reverse. If the lease ends mid-month — usually because the tenant gave notice and the lease term coincidentally ended on a non-month-end date, or because of mutual termination — pro-rate the last month using the same method specified for move-in. Mixing methods between the two is what produces the awkward sub-dollar disagreements that erode goodwill.

The two-second decision

Pick a method. Write it into your standard lease. Use it every time. The exact method matters less than the consistency. Tenants are not comparing pro-ration formulas across landlords; they want to know how the partial month was calculated and to see the math. A worked example in the lease addendum, with the daily rate spelled out, prevents nearly every dispute.

If you want a single recommendation: actual days, partial month upfront. It's slightly more in your favor on average, it matches how most accounting software prefers to book it, and it makes early termination math straightforward.