The second advance tax installment for Tax Year 2026-27 falls due on 15 September — routine, familiar, the same date it's always been. What's not routine is that this is the first year this deadline sits entirely under the Income-tax Act, 2025 rather than the 1961 Act, and a few genuinely practical wrinkles are worth knowing before you calculate the number.
Advance tax is the "pay as you earn" mechanism requiring anyone with a total tax liability of Rs 10,000 or more in a year — after TDS — to pay estimated tax in instalments through the year rather than in one lump sum at filing time. The schedule remains what it has always been: 15% of estimated liability by 15 June, 45% cumulative by 15 September, 75% cumulative by 15 December, and 100% by 15 March. None of that mechanical schedule has changed under the new Act.
What's Actually Different This Year
The genuine practical wrinkle sits in the surrounding provisions, not the schedule itself. The interest provisions for shortfall or deferment of advance tax — previously Sections 234B and 234C of the 1961 Act — have been renumbered and reorganised under the Income-tax Act, 2025, and if your business is estimating this year's liability using an internally built calculation sheet, tax software, or template carried over from last year, it's worth confirming that any section references baked into that tool have actually been updated, rather than assuming a working spreadsheet from last year needs no changes beyond updating the numbers. The underlying interest mechanism — roughly 1% per month on the shortfall — is materially the same, but a tool referencing the old section number in a way that affects a downstream calculation or disclosure is a real, if narrow, risk worth ruling out rather than assuming away.
The Bigger, More Common Mistake — Which Has Nothing to Do With the New Act
Separately from anything specific to this year's transition, this is a good moment to flag the mistake we see most often around the September instalment specifically: businesses and professionals with genuinely variable income — a services business with lumpy project billing, a professional whose income is heavily back-loaded toward the second half of the financial year — frequently underpay the September instalment by estimating conservatively off the prior year's pattern, only to have income materialise faster than expected later in the year. Because the September instalment requires 45% of your full-year estimate cumulatively, not just 45% of income actually earned so far, underestimating your full-year number at this stage compounds into instalment-based interest under the shortfall provisions even if the underlying number gets corrected by December.
What We'd Actually Recommend Before 15 September
If your income for this year is meaningfully different from last year's — genuinely up, genuinely down, or simply less predictable than usual — this is the instalment worth spending real time estimating properly, rather than defaulting to a percentage of last year's number out of habit. Recompute against your actual year-to-date trajectory and a realistic projection for the remainder of the year, not last year's filed return. And if you're using any calculation tool inherited from a prior year, take five minutes to confirm it reflects the current Act's section references correctly — a small, easy check against a genuinely avoidable, if narrow, transition-year error.