The national 2% or CPI cap (whichever is lower) governs a rent increase on a sitting tenant. It does not govern the rent you set for a brand-new tenancy or a permitted market-rent reset — that must not exceed market rent, and the accepted way to evidence market rent is with comparable dwellings from the RTB Rent Register: similar area, floor area, bedrooms and BER. TenantSync captures each unit's attributes (including BER) on the tenancy record and lets you attach up to three comparables to the rent-setting paperwork, so the justification is documented, not assumed — free 14-day trial, no card required.
Ask a busy agent what the legal rent for a property is and, since March 2026, the reflex answer is "last rent plus 2%." For a sitting tenant, that reflex is right. For a new let, it's the wrong question entirely — and the gap between those two situations is where a lot of rents are set incorrectly, in both directions.
Because the cap and the comparables answer two different questions. One asks how much more can I charge this tenant? The other asks what is this dwelling actually worth on the open market, and can I prove it? Treat the second like the first and you either leave money on the table or set a rent a tenant can challenge.
This is a guide, not legal advice
Rent-setting rules, the national cap, the treatment of market-rent resets and the RTB's requirements around comparable dwellings are detailed and fact-specific, and they changed with the March 2026 reforms. This article explains the general position for private residential tenancies. Confirm the current rules for your own tenancies with the RTB, and take advice on a contested rent, before acting.
Two different rent decisions
The single most useful thing to hold in your head is that "setting rent" is really two separate jobs with two separate rulebooks:
| The decision | What governs it |
|---|---|
| Increasing a sitting tenant's rent (an in-tenancy review) |
The national cap: the increase can't exceed the lower of 2% or inflation (CPI) since the rent was last set, reviewable once every 12 months, with a Notice of Rent Review served at least 90 days ahead and copied to the RTB the same day. |
| Setting rent for a new tenancy (or a permitted market-rent reset) |
Market rent: the rent must not exceed what the dwelling would command on the open market, evidenced by comparable dwellings from the RTB Rent Register — not by adding a percentage to a previous rent. |
The first is arithmetic; our national rent cap guide covers it end to end. The second is a judgement you have to be able to stand over — and that's what the comparables are for.
The cap protects a sitting tenant from a big jump. The comparables protect a new rent from being challenged. Knowing which question you're answering is half the job.
How the Rent Register comparables work
"Market rent" sounds subjective, but the RTB gives it an objective backbone: the RTB Rent Register and rent data, which record what tenancies are actually being let for across the country. To justify a new-tenancy rent, you point to comparable dwellings — recently let properties genuinely similar to yours — and their rents. It's often called a statement of comparators.
The word doing the work is comparable. A dwelling only supports your figure if it's genuinely like yours on the attributes tenants actually price:
- Same area. Location is the biggest single driver of rent — a comparable three streets away beats one in the next town.
- Similar floor area. A larger or smaller home isn't a like-for-like comparison.
- Same bedroom count. A two-bed and a three-bed are different products.
- Similar BER. Energy efficiency increasingly moves what a tenant will pay (more on this below).
The RTB's statement of comparators typically allows up to three comparable dwellings. Three well-chosen comparables — same area, same size, same bedrooms, similar BER — make a rent easy to defend. Three loose ones — right town, wrong size, wildly different BER — invite exactly the challenge you were trying to avoid.
Set market rent you can actually stand over
TenantSync keeps each unit's area, floor size, bedrooms and BER on the tenancy record, and its rent-setting workflow lets you attach up to three comparable dwellings as your statement of comparators — so a new-let rent is evidenced, not guessed.
No credit card required · Live in under 10 minutes
Why BER now affects comparables
BER — the Building Energy Rating — used to be an afterthought in a rent comparison. It isn't any more, for two reasons.
First, energy costs are part of the rent conversation. A well-insulated B-rated apartment is genuinely cheaper to live in than a draughty G-rated one of the same size, and tenants increasingly price that difference in. Two homes with the same floor area and bedroom count but very different BERs are not really the same product — so treating one as a comparable for the other weakens your justification.
Second, BER is now captured at RTB registration, which makes it a first-class attribute of a tenancy rather than a document in a drawer. That means it's available to sharpen a comparison — and, conversely, a comparison that ignores it looks less rigorous than one that accounts for it.
Treat BER as a comparison axis, not a formality
When you line up your three comparables, sanity-check their BERs against the subject property, not just their address and size. A comparable with a similar BER strengthens the case; one two or three bands off is worth a second look before you rely on it. TenantSync stores the BER rating on the property or unit so it's there when you need it.
A new tenancy vs a 6-year reset
The March 2026 reforms added a second moment where the market-rent question comes back: the end of a six-year cycle. Under the new Tenancy of Minimum Duration, a rent can be re-set to market rent at a cycle boundary — and, when a new tenancy begins, in specific permitted circumstances. Between those points, the 2% / CPI cap applies.
The practical consequence: the comparables exercise isn't only a move-in task. It comes around again at each permitted reset — which means the dwelling's attributes and its comparables are worth keeping on record from the start, so that when a reset window arrives you're not starting the justification from scratch.
One important limit on resets
A market-rent reset is not available after a 'no-fault' termination — ending a tenancy on a no-fault ground does not unlock a market reset for the next let. So before you reach for comparables at a change of tenant, confirm the reset is actually permitted in your circumstances. Confirm how the rules apply to you at rtb.ie.
Get the new-tenancy rent-setting checklist & comparables worksheet
Start a free 14-day trial and TenantSync captures each unit's area, bedrooms and BER, lets you attach up to three comparables to the rent-setting paperwork, and keeps the justification on the tenancy record for the next reset — the worksheet, built in.
Documenting the justification
Here's the part that separates a defensible rent from a lucky one: the justification is only worth what you can show. If a rent is ever questioned — by a tenant, or at the RTB — "it felt about right" is not a case. Three named comparable dwellings, with their rents, recorded against the tenancy at the time you set the rent, is.
That's why the market-rent decision belongs on the tenancy record, not in an email thread or someone's memory. Capture the dwelling's own attributes, capture the comparables you relied on, and keep them together — so the evidence exists before you need it, and travels with the tenancy to the next reset.
The mistakes that cost you
| Mistake | Why it costs you |
|---|---|
| Setting a new-let rent as "old rent + 2%" | The cap doesn't apply to a new tenancy — you can undershoot true market rent and lose income you were entitled to. |
| Assuming a reset is always available | A market reset is only permitted at certain points, and never after a no-fault termination — set one where it isn't allowed and the rent is challengeable. |
| Choosing loose comparables | Wrong area, size or BER weakens the justification — the comparables have to be genuinely comparable to carry weight. |
| Ignoring BER in the comparison | Comparing very different energy ratings treats unlike dwellings as alike and makes the case easier to contest. |
| Keeping no record of the justification | An undocumented market rent is hard to defend later — the evidence has to exist at the time the rent was set. |
None of these is about not knowing the market. They're about not proving it — asking the wrong question, or answering the right one without keeping the receipts. Both are fixable with a record.
How TenantSync helps
TenantSync is built so the market-rent decision is documented as a matter of course, not reconstructed after a dispute:
- The dwelling's attributes live on the record. Each property and unit carries its location, floor area, bedroom count and BER rating — the attributes that define what a genuine comparable looks like — so they're captured once and there whenever you set or reset the rent.
- Comparables attach to the paperwork. The rent-setting and Notice of Rent Review workflow lets you add up to three comparable dwellings (address and rent) as the RTB statement of comparators, so the justification is recorded with the notice rather than kept separately.
- The cap engine handles the in-tenancy side. For a sitting tenant, the same workflow checks a proposed increase against the 2% or CPI cap and produces a compliant Notice of Rent Review — with the 90-day timing and same-day RTB copy built in — so you use comparables for a new let and the cap for a review, correctly, each time.
- It carries to the next reset. Because everything is anchored to the tenancy, the attributes and the last justification are still there when a six-year reset window arrives.
It's the same platform that keeps every RTB registration on track, checks in-tenancy increases against the national cap, and tracks the six-year cycle that decides when a reset is even possible — on web, iOS and Android, so setting a legal, defensible rent is part of the workflow, not a separate research project.
How to get started
- Start your free 14-day trial — no credit card required.
- Add the property or unit with its area, bedrooms and BER — the attributes that define a comparable.
- Attach up to three comparables from the RTB Rent Register to the rent-setting paperwork for a new let or a reset.
- Use the cap engine for every in-tenancy review, and let the justification travel with the tenancy to the next reset.
Frequently asked questions
How do I set the rent for a new tenancy in Ireland?
For a brand-new tenancy the rent must not exceed market rent — what a willing tenant would pay on the open market. Unlike an increase on a sitting tenant, it isn't the old rent plus the national cap. The accepted way to evidence market rent is with comparable dwellings from the RTB Rent Register: properties in the same area, of similar floor area, bedroom count and BER, and their rents. Record those comparables so the figure is justified. General guidance, not legal advice — confirm at rtb.ie.
What's the difference between a new-tenancy rent and increasing a sitting tenant's rent?
An increase on a sitting tenant is capped: since March 2026 it can't exceed the lower of 2% or inflation (CPI) since the rent was last set. Setting the rent for a new tenancy, or a permitted market-rent reset, is a market-rent decision justified against comparable dwellings — not a percentage sum. Applying only the 2% cap to a new let can undershoot market rent; treating a reset as automatic can overshoot it and make the rent challengeable.
What are comparable properties on the RTB Rent Register?
Comparable properties — a statement of comparators — are recently let dwellings similar to yours, drawn from the RTB Rent Register, used to evidence that your rent reflects the market. To be genuinely comparable a dwelling should be in the same area and of similar type, floor area, bedroom count and BER. The statement of comparators typically allows up to three. Dwellings that aren't truly comparable weaken the justification.
Why does BER affect comparable rent now?
A dwelling's BER affects its running costs and therefore its market position, so two otherwise similar homes with very different BERs aren't truly comparable. As energy efficiency becomes a bigger factor in what tenants will pay — and with BER now captured at RTB registration — using comparables of a similar BER makes a market-rent justification more robust. TenantSync records BER on the property or unit alongside the other attributes that define a comparable.
How does TenantSync help justify market rent?
TenantSync captures each property or unit's attributes — location, floor area, bedrooms and BER — on the tenancy record, and its rent-setting and Notice of Rent Review workflow lets you attach up to three comparable dwellings (address and rent) as the RTB statement of comparators, alongside the rent-cap engine used for in-tenancy reviews. The justification is documented against the tenancy, on web, iOS and Android. General guidance, not legal advice; confirm at rtb.ie.