GST on Under-Construction Flats in Chennai (2026): What Buyers Actually Pay

Most buyers I meet in south Chennai know that GST has something to do with a flat purchase. Very few can tell you when it actually applies, at what rate, or on which part of the price. That gap costs money. I have watched buyers pay GST on a ready flat where none was due, and I have watched others budget for the wrong rate and walk into a nasty surprise at the agreement stage.

This is a practical read for anyone buying a residential flat in Velachery, Medavakkam, Sembakkam, East Tambaram or the surrounding belt in 2026. I will keep the tax jargon to a minimum and stay on what you, the buyer, end up paying and why. One caveat first. GST rates and thresholds are set by the GST Council and they do change. Treat the figures here as the current framework and confirm the latest position with your developer's tax team or a chartered accountant before you sign.

And a clarification that matters more than people realise. GST is a completely separate charge from stamp duty and registration. Two different taxes, two different authorities, two different things being taxed. Get that straight and half the confusion disappears on its own.

When GST applies, and when it does not

This is the single most important distinction in the whole subject. GST applies only to flats sold while they are still under construction. Once a building receives its completion certificate from the competent authority and the flat is genuinely ready to occupy, a sale of that flat does not attract GST at all.

The logic behind it is simple enough. GST is a tax on the supply of construction services. If the construction is already finished and certified before you enter the sale, no ongoing service is being supplied to you, so there is nothing to tax. You are buying immovable property, not construction work.

In practice this splits your options cleanly. New flats from a builder that are still going up: GST applies. Resale flats and completed inventory sold with a completion certificate: no GST. If you are weighing those two paths, the tax treatment is one more input, and it sits alongside the other trade-offs in our guide on resale versus new construction flats.

The two GST rates: affordable and standard

For under-construction residential flats there are broadly two effective rates, and both apply without input tax credit. I will explain the input tax credit point on its own, because it trips people up.

• Affordable housing: an effective rate of around 1% on the construction value, with no input tax credit. This applies only where the flat clears both the value and carpet-area thresholds for affordable housing, explained further down.
• Other residential units: an effective rate of around 5% on the construction value, again with no input tax credit. This is the standard rate for under-construction flats that fall outside the affordable bracket.

So a regular 2 or 3 BHK in most of south Chennai that is still under construction will typically attract the 5% rate, because the ticket sizes, and sometimes the carpet areas, put it outside the affordable definition. A genuinely budget unit that fits inside both thresholds can qualify for the 1% rate. Confirm in writing which bracket your specific flat falls into, because it moves the number meaningfully.

What "without input tax credit" actually means for you

Under the current scheme the builder pays GST on cement, steel and other inputs but cannot pass that credit on to reduce your bill. The rates above are already the net effective rates the buyer faces. You do not get a separate credit, and the builder is not supposed to add GST on top of these and then also claim the input credit. From your side the takeaway is plain: the rate you pay on the construction value is the rate, and there is no further GST adjustment to chase in your favour.

What actually qualifies as affordable housing

This is where buyers get optimistic and assume their flat qualifies for the 1% rate because it feels affordable. The definition is specific, and a flat has to satisfy two conditions together, not just one.

• Value threshold: the total consideration for the flat must stay within the prescribed cap, commonly cited at up to 45 lakh. How Chennai is classified, and therefore the exact ceiling that applies to your project, should be confirmed for your case.
• Carpet area threshold: the carpet area must stay within the prescribed limit, typically up to 60 sq m, roughly 645 sq ft, in metropolitan areas, and up to 90 sq m in non-metropolitan areas.
• Both must be met: miss either the value cap or the carpet-area limit and the flat is treated as standard residential at the higher rate, not affordable.

Notice that the limit is on carpet area, the actual usable space inside your walls, not the super built-up area printed on the brochure. Many south Chennai flats are sold on a saleable or super built-up basis that runs noticeably larger than the carpet area, so it pays to know the difference. If those terms feel fuzzy, read our explainer on carpet area versus saleable area before you assume which bracket applies.

How GST is applied on the construction component

GST on an under-construction flat is charged on the value of the construction supplied to you, broadly the agreement value attributable to the building, with the standard treatment that sets aside a portion as the land component. The undivided share of land you buy is not a supply of construction service, so it is handled differently from the bricks-and-mortar value.

The cleanest way to handle this as a buyer is to ask the developer for a written breakdown: the construction value, the GST rate being applied, the rupee amount of GST, and the schedule on which it is collected. Under-construction flats are usually paid in stages tied to construction milestones, and GST is collected on each instalment as it falls due rather than in one lump. Get that payment schedule into the agreement so nothing springs up mid-project.

A rough worked example

Take a notional under-construction flat with a construction value of, say, 50 lakh that sits in the standard bracket. At an effective 5%, the GST works out to roughly 2.5 lakh, spread across the payment stages. If the same flat qualified as affordable at 1%, it would be closer to 50,000. These are round figures purely to show the scale of the gap between the two brackets. Your actual number depends on how the construction value is computed in your specific agreement, so use the developer's figure, not mine.

GST is separate from stamp duty and registration

Worth repeating, because it is the single biggest source of confusion. GST and stamp duty are not the same charge, and you are not being taxed twice on the same thing in the way people fear. They run side by side.

• GST is a tax on the supply of construction services, charged only on under-construction flats, paid to the developer who then remits it to the government.
• Stamp duty and registration charges are levied by the Tamil Nadu government on the registration of the sale document itself, calculated on the higher of the agreement value or the guideline value, and paid at the sub-registrar's office.
• Both can apply to the same purchase. An under-construction flat can attract GST on the construction component and stamp duty plus registration on the registered conveyance. A completed flat with a completion certificate attracts stamp duty and registration but no GST.

Because stamp duty and registration follow an entirely separate set of rules and rates, I have deliberately kept them out of this post. For the current Tamil Nadu rates and how guideline value drives the calculation, see our dedicated guide on stamp duty and registration charges. Budget for both GST and registration costs together when you work out your total outflow, because together they add a real percentage on top of the headline flat price.

Common buyer mistakes and misunderstandings

After years of closing these transactions, the same errors come up again and again. Most are avoidable with one or two questions asked early.

Paying GST on a ready flat

The most expensive mistake. If the building holds its completion certificate and you are buying a finished unit, GST should not be on your bill. Always ask whether the completion certificate has been issued before you accept any GST line item.

Assuming the affordable rate applies

Buyers see 1% quoted somewhere online, budget for it, then find their flat sits in the 5% bracket because it crosses the value cap or the carpet-area limit. Confirm your bracket in writing before you fix your budget.

Confusing GST with stamp duty

Treating the two as one charge, or assuming that paying one covers the other. They are separate. Account for both.

Not getting the breakdown in writing

A verbal assurance about the rate is worthless if the agreement says something else. Insist on the construction value, the rate, the rupee amount and the collection schedule being documented.

How this fits the wider buying decision

GST is one line in a longer cost sheet, but it can swing your total outlay by a meaningful amount, especially on a new under-construction project at the 5% rate. It also quietly favours completed and resale inventory, where GST simply does not arise. That does not automatically make ready flats the better buy, since construction-linked payment plans and newer specifications carry their own appeal, but it is a real factor to weigh rather than wave away.

Whatever you decide, do the arithmetic with the actual rate that applies to your flat, keep GST and registration as separate lines, and verify the current rules before you commit. Tax rules move, and what held last year may have shifted.

In short

• GST applies only to under-construction flats. Completed flats sold with a completion certificate attract no GST.
• The two effective rates are roughly 1% for affordable housing and 5% for other residential units, both without input tax credit.
• Affordable housing needs both the value cap and the carpet-area limit to be met. Miss either and the standard rate applies.
• GST is charged on the construction value and is entirely separate from stamp duty and registration.
• Get the rate, amount and schedule in writing, and confirm the latest rules before you sign.

For related reading, see our guides on resale versus new construction flats, stamp duty and registration charges, the property documents field checklist, and carpet area versus saleable area. If you want help working out the full cost sheet on a specific flat, reach out to our team.