Prorated rent is the partial-month charge a tenant pays when they move in or out on a day other than the first of the month. The math itself is simple division. What trips landlords up in Massachusetts is the question underneath it: who decides the method, and is proration even required? The short answer is that for a normal mid-month move-in, no statute forces you to prorate at all — the written lease controls. When a tenancy-at-will ends mid-month, the answer depends on who ends it and why: an ordinary termination by either party's notice is governed by MGL c.186 §12 plus the lease and rent period, while a no-fault termination — one that happens without the tenant's fault, by operation of law or by an act of the landlord — falls under MGL c.186 §13, which limits what the tenant owes to the days actually occupied.
This guide walks through when proration applies, the two methods landlords use, what the law and the lease each control, and three worked examples covering both move-in and move-out.
1. The short answer
- Move-in (mid-month): Massachusetts has no statute that requires a landlord to prorate the first month. Whether you charge a full month or a partial month, and which method you use, is governed by the written lease. In practice, nearly every lease prorates the first partial month, and a clear lease clause stating the method is what prevents a dispute.
- Move-out at the end of a fixed-term lease: the tenant owes rent through the end of the term. There is generally nothing to prorate unless the lease or a written agreement says otherwise.
- Ordinary termination of a tenancy-at-will (either party's notice): governed by MGL c.186 §12, which sets the notice required to terminate an estate at will (for rent payable at intervals under three months, an interval equal to the rent period or 30 days, whichever is longer — so weekly rent still needs 30 days — or the 14-day notice to quit for nonpayment with its cure rule). What the tenant owes through the termination date follows from §12's timing plus the lease and the rent period — not from §13.
- No-fault termination of a tenancy-at-will: MGL c.186 §13 applies when a dwelling tenancy-at-will is terminated without the fault of the tenant — by operation of law or by an act of the landlord (other than under §12). In that situation the tenant "shall be liable to pay rent for such time during the said period as he occupies or retains the premises, at the same rate as theretofore payable." That is a statutory limit on the tenant's liability — a ceiling that caps what the tenant owes to actual occupancy at the existing rate.
The recurring theme: proration on the way in is a lease question; an ordinary move-out is a §12-plus-lease question; and a no-fault move-out is a §13 statutory ceiling on the tenant's liability.
2. Is prorated rent required by Massachusetts law?
There is no Massachusetts statute that says "a landlord must prorate the first month's rent." For a move-in, the obligation comes from the lease, not the General Laws. If the lease is silent and the tenant takes possession on the 15th, the parties' agreement (or their conduct) decides whether the tenant pays a half-month or a full month — there is no statutory default that prorates it for them.
The picture changes when a tenancy-at-will ends. How it changes depends on how it ends. An ordinary termination — either party serving the notice required to end an estate at will — is governed by MGL c.186 §12. §12 sets the notice (for rent payable at intervals under three months, the rent-period interval or 30 days, whichever is longer; or a 14-day notice to quit for nonpayment, which the tenant can cure by paying within 10 days if no similar notice issued in the prior 12 months); what the tenant owes through the termination date then follows from that timing plus the lease and the rent period.
A different statute governs the no-fault case. MGL c.186 §13 applies when a dwelling tenancy-at-will is terminated without the fault of the tenant — "either by operation of law or by act of the landlord, except as provided in section twelve." In that situation the statute provides that the tenant "shall be liable to pay rent for such time during the said period as he occupies or retains the premises, at the same rate as theretofore payable." In plain terms: on a no-fault termination, the tenant's liability is measured by the days actually occupied at the existing rent rate — a de facto proration that the statute imposes as a ceiling on what the landlord can collect.
3. Can my landlord charge a full month for a partial month?
At move-in: potentially yes, if the lease says so. Because no statute mandates first-month proration, a lease that requires a full month's rent for a partial first month is a contract term, and Massachusetts has no specific statutory prohibition on it the way it does for, say, charging a late fee before day 31 under §15B(1)(c). That said, charging a full month for a few days of occupancy is uncommon, hard to defend as good practice, and a frequent source of friction. The clean approach is a lease clause that prorates the first partial month and states the method.
At move-out of a tenancy-at-will: it depends on how the tenancy ended. In a no-fault termination — without the tenant's fault, by operation of law or by an act of the landlord — §13 limits the tenant's liability to the time actually occupied at the existing rate, so the landlord cannot collect a full month from a tenant who vacates mid-month. In an ordinary termination by either party's notice under §12, §13's cap does not apply; what the tenant owes through the termination date is set by §12's timing and the lease/rent period, and in practice a tenancy-at-will rent obligation runs to the effective termination date rather than the full remaining month.
4. The two calculation methods
Two methods dominate, and the difference between them is the denominator.
Method A — 30-day flat (the "banker's month")
Treat every month as 30 days regardless of its actual length.
Daily rent = Monthly rent ÷ 30
Prorated rent = Daily rent × Number of days occupied
This method is simple and predictable, and it is the most common one in residential lease clauses. Its quirk is that it slightly overcharges in 31-day months and slightly undercharges in February.
Method B — Actual days in the month
Use the real number of days in the specific month.
Daily rent = Monthly rent ÷ (Actual days in that month)
Prorated rent = Daily rent × Number of days occupied
This method is more precise — the daily rate matches the month you are actually in — and it is the method many tenants and tenant advocates view as the fairest because it never charges more than 1/28th to 1/31st of rent per day depending on the month.
5. Worked example 1 — mid-month move-in (January 15)
Rent is $1,800/month. The tenant takes possession on January 15 and occupies through January 31 — that is 17 days (the 15th through the 31st, inclusive).
30-day flat method:
Daily rent = $1,800 ÷ 30 = $60.00
Prorated rent = $60.00 × 17 = $1,020.00
Actual-days method (January has 31 days):
Daily rent = $1,800 ÷ 31 ≈ $58.06
Prorated rent = $58.06 × 17 ≈ $987.10
The 30-day method charges about $33 more here because January is a 31-day month. Neither is "wrong" — but the lease should say which one applies so the tenant isn't surprised.
6. Worked example 2 — no-fault mid-month termination (February 20, §13)
This is a §13 no-fault scenario — the kind §13 actually governs. §13 reaches no-fault terminations "by operation of law or by act of the landlord, except as provided in section twelve" — so the trigger here is not an ordinary §12 termination notice (those run through §12), but something like a tenancy ended by operation of law (for example, the unit is condemned by the building inspector, or title passes in a way that terminates the at-will tenancy). Rent is $1,800/month, paid on the first. The tenant has done nothing wrong; the tenancy ends and the tenant vacates February 20, occupying February 1 through February 20 — that is 20 days.
Under MGL c.186 §13, because the termination is without the tenant's fault, the tenant is liable only for the time actually occupied at the existing rate. If the tenant already paid the full $1,800 on February 1, the landlord owes back the unoccupied portion.
Actual-days method (February 2026 has 28 days):
Daily rent = $1,800 ÷ 28 ≈ $64.29
Rent owed (20 days) = $1,800 ÷ 28 × 20 ≈ $1,285.71
Refund to tenant = $1,800 − $1,285.71 ≈ $514.29
Because §13 caps liability at actual occupancy, the landlord cannot keep the full February rent. The unoccupied 8 days come back to the tenant. (This is separate from the security-deposit return clock — see Section 11.)
Note the contrast with an ordinary tenant-given termination: if the tenant had instead given notice ending the tenancy under §12, §13's liability cap would not be the controlling rule. What the tenant owes through the termination date in that case follows from §12's notice timing and the lease/rent period rather than from §13.
7. Worked example 3 — late-month move-in (March 25)
Rent is $2,100/month. The tenant moves in March 25 and occupies through March 31 — that is 7 days.
30-day flat method:
Daily rent = $2,100 ÷ 30 = $70.00
Prorated rent = $70.00 × 7 = $490.00
Actual-days method (March has 31 days):
Daily rent = $2,100 ÷ 31 ≈ $67.74
Prorated rent = $67.74 × 7 ≈ $474.18
A late-month move-in is where the two methods diverge most as a percentage of the small partial charge — another reason to state the method in the lease.
8. What if there's no written lease?
A tenancy with no written lease is, in Massachusetts, typically a tenancy-at-will — a month-to-month arrangement created by the parties' conduct and the payment of rent. There is no lease clause to set a proration method, so:
- At the start, the tenant pays for the period agreed; if they take possession mid-month, the practical norm is to prorate, but the method is whatever the parties agree to because no statute fixes it.
- At termination, the governing rule depends on how the tenancy ends. An ordinary termination by either party's notice runs through MGL c.186 §12 — the notice timing plus the rent period set what the tenant owes through the termination date. A no-fault termination (without the tenant's fault, by operation of law or by an act of the landlord) runs through MGL c.186 §13, which limits the tenant to the time actually occupied at the existing rate.
The absence of a written lease makes the statute more important on the way out, not less, because there is no contract term filling the gap — §12 supplies the notice rules for an ordinary termination, and §13's liability cap controls a no-fault one.
9. Move-out proration after a notice to quit
A valid, uncured notice to quit can terminate a tenancy-at-will, but the result is not automatic. Under §12, the notice has to meet the statute's timing and content requirements — for nonpayment, a 14-day notice to quit that the tenant can defeat by paying the rent due within 10 days (if no similar notice issued in the prior 12 months). One wrinkle on the content requirement: §12 provides that if the nonpayment notice omits the required cure-rights language, that omission doesn't void the notice — it extends the tenant's cure deadline to the date the answer is due in any later summary process. Either way, a notice the tenant cures does not end the tenancy.
When termination is ordinary — by either party's §12 notice — what the tenant owes through the termination date follows from §12's timing and the lease/rent period; §13's liability cap is not the controlling rule. §13 governs the no-fault case instead: when a tenancy-at-will is terminated without the tenant's fault, by operation of law or by an act of the landlord, §13 limits the tenant's liability to actual occupancy at the existing rate, so proration to actual days follows from the statute once the termination takes effect.
For a fixed-term lease, the analysis is different again. The tenant generally owes rent through the end of the term regardless of when they physically leave, unless the lease provides for early termination or the parties agree otherwise. A landlord does have a duty to mitigate damages by attempting to re-rent, but that is a damages question, not a proration question. Do not assume a fixed-term move-out automatically prorates the final month — it usually does not.
10. City-specific rules — Boston, Cambridge, Somerville
None of the major Massachusetts cities mandates a specific proration method beyond what state law provides. Local ordinances in Boston, Cambridge, and Somerville address registration, inspection, and (in some cases) rent-related notice requirements, but they do not impose a proration formula that overrides the lease, §12, or §13. The lease still controls the move-in method, §12 still governs ordinary tenancy-at-will terminations, and §13 still caps liability on a no-fault termination. If you operate in Boston, the more pressing city-specific obligation is annual rental registration — see our Boston rental registration checklist.
11. What your lease should say to avoid disputes
The cleanest way to prevent a proration dispute is a lease clause that states the method and the day count rule. A workable structure:
Prorated rent for any partial month shall be calculated by dividing the monthly rent by [30 / the actual number of days in that month] and multiplying by the number of days the tenant occupies the premises during that month. The first day of occupancy counts as a full day.
Pick one denominator and name it. Stating whether the move-in day counts removes the most common off-by-one disagreement. And keep proration separate from the security-deposit accounting — the partial-month rent is a rent charge, not a deposit item, and conflating the two creates §15B exposure. For the full deposit picture, see our MA security deposit law for landlords guide.
12. Common mistakes
- Assuming proration is legally required at move-in. It isn't — the lease controls. If the lease is silent and you want to prorate, document the agreed method in writing before move-in.
- Charging a full month after a no-fault tenancy-at-will termination. When the tenancy ends without the tenant's fault (by operation of law or an act of the landlord), §13 caps the tenant's liability at actual occupancy. Keeping the full month in that situation is overcollection. (In an ordinary §12 termination by notice, the obligation instead runs to the termination date under the lease and rent period.)
- Mixing up the two methods between move-in and move-out. Use the same lease-stated method consistently; switching denominators looks like manipulation.
- Off-by-one day counts. Decide whether the move-in/move-out day counts and state it in the lease. Inclusive vs exclusive counting is the single most common source of small disputes.
- Treating a fixed-term final month like a tenancy-at-will. A fixed-term tenant generally owes through the end of the term; the final month usually does not prorate just because they left early.
13. How Tenvale helps
Tenvale calculates prorated rent automatically when you set a mid-month lease start or end date — it shows the day count, applies the method you choose, and writes a clean rent charge to the ledger so the partial month never gets tangled up with the security-deposit accounting. The §13 no-fault move-out limit and the §15B deposit clocks live in the same system, so the partial-month math doesn't have to be reconciled by hand.
14. Sources cited in this article
- MGL c.186 §12 (termination of an estate at will by notice; 14-day nonpayment notice + cure)
- MGL c.186 §13 (no-fault tenancy-at-will termination; tenant liability limited to time occupied)
- MGL c.186 §15B (security deposit; includes §15B(1)(c))
Statutory text is updated periodically. Always verify the current version before relying on a citation.