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Prorated Rent Formula

The standard prorated rent formula is: (monthly rent ÷ days in the month) × days you occupy the unit. That's it — find the daily rate, count your days, multiply. The only thing that changes between landlords is how the daily rate is computed: three methods are in common use, and they can shift the same move-in by $20–$30. This guide compares all three with worked examples so you can match any landlord's number — or defend your own.

TL;DR

Standard formula: (rent ÷ days in month) × days occupied. Alternatives: rent ÷ 30, or rent × 12 ÷ 365. Use whichever your lease names; round only the final total.

The three proration methods, compared

Comparison of the three prorated rent methods
MethodDaily rate formulaBest forQuirk
Actual days in monthrent ÷ 28, 29, 30, or 31Fairness — matches the calendarDaily rate changes every month
30-day monthrent ÷ 30Simplicity — one rule all yearSlightly off in Feb and 31-day months
365-day year(rent × 12) ÷ 365One constant daily rateIgnores month lengths entirely

Method 1 — Actual days in the month (most common)

Daily rate = monthly rent ÷ the real number of days in that month. January divides by 31, April by 30, February by 28 (or 29 in a leap year). This is the default in most residential leases because it's the hardest to argue with: the rate follows the calendar.

($1,500 ÷ 31) × 17 = $822.58
A January 15 move-in on a $1,500 lease: 17 days at $48.3871/day.

Method 2 — 30-day month

Daily rate = monthly rent ÷ 30, every month. February, April, January — all treated as 30 days. Large property managers like it because one rule covers the whole portfolio and tenants can verify the math without a calendar.

($1,500 ÷ 30) × 17 = $850.00
Same January 15 move-in: 17 days at exactly $50/day. Note the tenant pays $27.42 more than with actual days here.

Method 3 — 365-day year

Daily rate = (monthly rent × 12) ÷ 365. The full year's rent is spread evenly across 365 days, giving one daily rate that never changes. It's the least common in residential leases but appears in corporate and extended-stay housing.

($1,500 × 12 ÷ 365) × 17 = $838.36
Same dates: 17 days at $49.3151/day — landing between the other two methods, as it usually does.

4 worked examples

Example 1 — Actual days: $1,200 rent, March 10 move-in

March has 31 days; March 10–31 is 22 days. $1,200 ÷ 31 = $38.7097/day. $38.7097 × 22 = $851.61.

Example 2 — 30-day method: same dates

$1,200 ÷ 30 = $40.00/day, exactly. $40.00 × 22 = $880.00 — $28.39 more than the actual-days result, purely from the simpler denominator.

Example 3 — 365-day method: same dates

$1,200 × 12 ÷ 365 = $39.4521/day. $39.4521 × 22 = $867.95, again between the other two.

Example 4 — Leap-year February: $2,400 rent, February 15, 2024

February 2024 has 29 days; February 15–29 is 15 days. $2,400 ÷ 29 = $82.7586/day. $82.7586 × 15 = $1,241.38. In non-leap 2026 the same move-in would be 14 days ÷ 28 = $1,200.00 — the leap day changes both inputs at once.

The rounding rule everyone gets wrong

Round only the final total to the nearest cent — never the daily rate. Rounding the daily rate first creates penny errors that compound: $1,000 ÷ 31 = $32.2581/day, and 17 days is $548.39, but rounding the rate to $32.26 first gives $548.42. Three cents sounds trivial until a property manager repeats the mistake across 200 units.

Try it yourself: run any of these examples through the free prorated rent calculator — it keeps full precision until the last step and shows every line of the math with your numbers.

Formula FAQs

What is the standard prorated rent formula?
The most widely used formula is: (monthly rent ÷ days in the month) × days occupied. For a $1,500 lease with a January 15 move-in: ($1,500 ÷ 31) × 17 = $822.58. Two alternatives exist: the 30-day method (rent ÷ 30 × days) and the 365-day method (rent × 12 ÷ 365 × days).
When should a landlord use the 365-day method?
The 365-day method suits landlords who want one constant daily rate all year instead of a rate that changes every month. It gives slightly lower daily rates in 31-day months and slightly higher ones in February compared with the actual-days method. It must be named in the lease — don't switch methods mid-tenancy without agreement.
Is the 30-day method fair to tenants?
Mostly yes, with small quirks. In 31-day months the tenant pays slightly more than the actual-days method ($850 vs $822.58 on a $1,500 January 15 move-in); in February the tenant pays slightly less ($950 vs $1,017.86 for a February 10 move-in). The differences run a few dollars either way, which is why many leases accept the 30-day method for its simplicity.
Do leap years change the formula?
Only for the actual-days method, and only in February: divide by 29 instead of 28. A $1,500 lease with a February 10 move-in costs $1,034.48 in leap year 2024 versus $1,017.86 in 2026. The 30-day and 365-day methods ignore leap years entirely.
Should the daily rate be rounded before multiplying?
No. Round only the final total to the nearest cent. Rounding the daily rate first introduces penny errors — for example, $1,000 ÷ 31 = $32.2581 per day, and 17 days is $548.39, but rounding the rate to $32.26 first gives $548.42. This calculator keeps full precision until the last step.
What if my lease doesn't name a method?
Default to the actual-days-in-the-month method — it's the most defensible because it matches the calendar exactly. Then ask your landlord to confirm the method in writing before you pay. If you can't agree, your state's tenant association or a local housing clinic can tell you what courts in your area normally accept.

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