Bill Proration Calculator (move-in / move-out)

Understanding the bill proration calculator — concept and principle

When you move in or out partway through a billing period, the utility, internet or service charge for that period has to be split fairly between you and the other occupant, landlord or buyer. Proration does this by charging each party only for the days they were responsible. The same method is used for rent in a partial month, shared bills between housemates who changed, and settlement adjustments when a property is sold.

Turn the bill into a daily rate, then multiply by each person’s days.

How it is calculated

Per day = bill amount ÷ days in billing period.
Your share = bill × your days ÷ days in period.
Other party's share = bill × (days in period − your days) ÷ days in period.

The two shares always add up to the full bill.

The principle

Proration assumes the charge accrues evenly over time: every day of the period costs the same. That is exactly true for fixed charges such as a standing charge, a subscription or rent, and a reasonable approximation for usage-based bills when no meter reading was taken on the moving day. The daily rate is the bill divided by the days it covers, and each party pays daily rate × their days. Be consistent about whether the moving day itself counts for you, the other party, or is shared.

Worked example

Inputs: bill $120, 30-day billing period, you are responsible for 12 days.
Per day: 120 ÷ 30 = $4.00.
Your share: 120 × 12 ÷ 30 = $48.00.
Other party: 120 × (30 − 12) ÷ 30 = 120 × 18 ÷ 30 = $72.00.
Check: 48 + 72 = 120.

Each point is the calculator re-run with only “Days in billing period” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Days in billing period	Your share
7.5	$192.00
15	$96.00
22.5	$64.00
30	$48.00
37.5	$38.40
45	$32.00
60	$24.00

How to read the result

Your share is what you owe or should be reimbursed. If you already paid the whole bill, the other party owes you their share. For usage-based bills (electricity, gas, water) a meter reading on the moving day is fairer than time-based proration, especially when usage was unusual, for example an empty property or a winter heating month. Count days from the bill's actual period dates, not from the calendar month.

Common mistakes

Using 30 days for every bill instead of the true number of days in the billing period.
Counting the moving day twice, or not at all.
Prorating the whole bill when it includes a one-off connection fee or a previous balance that belongs to one party.
Splitting a usage charge by days when meter readings are available.

Keep in mind: Time-based proration is an even-usage approximation. Leases, sale contracts and utility providers may set their own rules; follow the contract where it specifies a method.

Frequently asked questions

Should I use 365 or 360 days for rent proration?

Contracts vary; some use the actual days in the month, others a yearly daily rate. Use the method your lease states.

Does the move-in day count?

Usually the person who has the keys on that day pays for it, but agree on this in writing.

How do I prorate for three people?

Calculate each person's days separately and multiply the daily rate by each, making sure the days add up to the period.

Sources: Consumer Financial Protection Bureau — Closing Disclosure explainer (prorations and adjustments)

Checked 8 Nov 2026. Typical coverage rates and standard formulas. Always check the product label and local building rules; buy 5–10% extra for waste.

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