Old regime or new: the deduction total where it flips

How the two Indian income tax regimes differ, the deduction total at which the old regime wins, and how to work out which one costs you less this year.

The short answer: India offers two income tax regimes: an older one with lower headline treatment of income but a long list of deductions and exemptions, and a newer one with a simpler, generally lighter rate structure and almost none of them. Which costs you less is a single arithmetic question — compute your tax under both using the current year's rates and your own actual deductions, and pick the smaller number. There is a break-even level of total deductions above which the old regime wins, and below which the new one does; that level moves every year with the rates, which is why the answer has to be recomputed annually rather than decided once.

Key points

The choice is arithmetic, not strategy: compute both with this year's rates and your real deductions, then pick the lower.
A break-even deduction total exists each year — above it the old regime wins, below it the new one does.
Only count deductions you would genuinely claim; an investment made solely to justify a regime is a cost, not a saving.
The break-even moves whenever the rates or limits change, so this is an annual decision rather than a permanent one.

What actually differs between them

The two regimes are not two rate cards on the same base. They differ in what is taxable before the rates are applied at all, which is why comparing headline rates tells you nothing.

The structural difference
	Old regime	New regime
Rate structure	Higher at comparable levels	Generally lighter
Deductions and exemptions	A long list available	Almost none
Complexity	Requires records and planning	Little to compute
Who it favours	High claimers of deductions	Low claimers of deductions

The specific rates, slab boundaries and which deductions survive in each regime change with each Finance Act. Take them from the Income Tax Department for the year you are computing.

So the comparison is between two different taxable incomes taxed at two different rate cards. That is a calculation rather than a preference, and it is why a colleague's answer is not evidence about yours.

Finding your break-even

For any income there is a total deduction figure at which the two regimes cost the same. Below it the new regime is cheaper; above it the old one is. Finding your own is a four-step exercise.

Total your genuine deductions. Retirement contributions you already make, insurance premiums you already pay, home loan interest, rent exemption if applicable. Only what you would claim regardless of the regime.
Compute tax under the old regime on income less those deductions, using this year's old-regime rates.
Compute tax under the new regime on income with only the deductions that survive there, using this year's new-regime rates.
Compare, and note the gap. If it is small, the simpler regime is worth something on its own; if it is large, the arithmetic decides.

What moves the answer between years

Rate or limit changes. Any Finance Act adjustment to either regime moves the break-even, sometimes substantially.
A home loan starting or ending. Interest is usually the largest single deduction available, so taking one on or paying it off can flip the answer in either direction.
A change in rent or in city. Where a rent-based exemption applies, moving cities can change the deduction total materially.
A large income change. The break-even is a deduction total, but its position relative to your income shifts as income moves through the slabs.

Because all four are common, treat the regime choice as an annual ten-minute recomputation rather than a decision made once and inherited. Any of these events on its own is enough to reverse last year's answer.

The other half of understanding your own tax is understanding what your employer deducts before you ever see the money — see CTC versus take-home.

One practical point about timing. Employers ask for a regime declaration early in the financial year and compute your monthly TDS from it, so a declaration made carelessly in April changes your take-home for twelve months. It is usually possible to correct the position when the return is filed, but that means either a refund you waited a year for or a shortfall to settle at once — neither of which is as good as spending ten minutes on the comparison before the declaration is due.

Budget Builder: Whichever regime you land on changes one number that matters more than the tax itself: what actually reaches your bank account each month. Put that figure into the Budget Builder and the difference between the two regimes stops being an abstraction and becomes a line in your month.

Frequently asked questions

Which regime should I choose?

Whichever produces the lower tax on your own numbers for the current year — there is no general answer, because it depends entirely on how much you genuinely claim in deductions. Broadly, someone with a home loan, substantial retirement contributions and rent exemption tends toward the old regime; someone with few deductions tends toward the new one. Compute both rather than reasoning about which type you are.

Can I switch between regimes?

Salaried taxpayers without business income have generally been able to choose each year, while those with business income face tighter restrictions on switching back. The rules on this have changed more than once, so confirm the current position on the Income Tax Department site for the assessment year in question before relying on being able to switch.

Should I invest specifically to save tax?

Only where you would want the investment anyway. A tax deduction reduces the cost of an investment; it does not make a poor one good. Locking money into an instrument with a mediocre post-tax return and a long lock-in in order to reduce this year's tax is a decision that looks sensible in March and looks expensive for the following five years.

Sources

Income Tax Department — current rates, slabs and deductions