What this is doing
The engine unfolds your CTC into basic (40% of CTC), HRA, employer PF, and gratuity, then arrives at gross. Employer NPS inside CTC is part of taxable salary, then deducted under 80CCD(2); it is not cash. The old regime subtracts the ₹50k standard deduction, Professional Tax, HRA exemption, and your 80C/80D/NPS/24(b) deductions; the new regime subtracts ₹75k and employer NPS (capped at 14% of basic) — not PT or 80CCD(1B), which s.115BAC disallows. Take-home is cash salary minus employee PF, professional tax paid, employee NPS, and income tax. Each remainder is run through the regime's slabs, with the 87A rebate (₹12L threshold new, ₹5L old, marginal relief to ₹12,70,588), surcharge marginal relief on ordinary salary income, and a 4% cess. The "wins" banner and the saving are simply the gap between the two tax totals.
Slab tax is computed by marching taxable income across the band limits and multiplying each slice by its rate — no lookups, pure arithmetic.
Worked example — the default inputs
CTC ₹15,00,000. Mumbai (metro). Rent ₹25,000/month. Below 60. 80C ₹1,50,000, 80D ₹25,000, NPS 1B ₹50,000, employer NPS ₹60,000.
- Basic ₹6,00,000, gross ₹14,49,540 (after PF ₹21,600 and gratuity ₹28,860)
- Old taxable income ₹8,72,140 → tax + cess ₹90,405 → annual take-home ₹12,25,135
- New taxable income ₹13,14,540 (PT and 80CCD(1B) not deducted from tax) → tax + cess ₹80,268 → annual take-home ₹12,35,272
- New regime wins on tax by ₹10,137. Cash still subtracts employee PF ₹21,600, professional tax ₹2,400, employee NPS ₹50,000 and employer NPS ₹60,000 from gross.
Raise the salary and the old regime's deductions weigh less — but the tool lets you see that flip instead of assuming it.
Estimate only
Your actual tax depends on the real salary structure in Form 16, your HRA as paid, and every deduction you can prove — not the 40/50/40 split this tool assumes. Use it to pick a regime, then get a CA to reconcile the filing number.