See the old-regime deduction hurdle on your income, then add the HRA, home loan, 80C and NPS money you would actually use and see whether the old regime catches up.
Why does this page lead with a rupee hurdle instead of naming the better regime?
Because whether you will clear that hurdle is a fact about you, not about our arithmetic. The maths can tell you the deduction the old regime needs and how much your actual plan contributes. It cannot tell you whether you really want to lock that money into PPF, NSC, a tax saver deposit or NPS.
Why is there both a total hurdle and a shortfall?
The total hurdle is the old-regime deduction that would make the two regimes equal on this income. The shortfall is how much of that line your real facts still do not cover after HRA, home loan interest, health cover, 80C already used, and the new money you would actually invest. The first says where the line is. The second says how far away you are.
Why does 80C not decide the regime on its own?
Because 80C is capped and the tax saving is always smaller than the money you lock up. If the line says you need ₹1,50,000 more of 80C, that only tells you the deduction the old regime needs. It does not say every 80C product is a good investment, and it definitely does not say locking ₹1,50,000 to save less than that is a win.
Why is NPS treated separately from the rest of 80C?
Because part of NPS sits inside 80C and part of it can reach the extra ₹50,000 under 80CCD(1B). That extra deduction is the strongest tax argument for NPS, and PPF cannot match it. But NPS also locks part of the corpus into an annuity, so the deduction is only half the question. This page shows both halves together.
What does this page hold fixed?
Your income, HRA, home loan interest, health cover, 80C already used, and the new money you would actually place. Move any of those and the line moves with them. The 80C route and the NPS route each have their own page because the product choice and the return assumption are separate questions from the regime line itself.
Why are the NPS return and annuity rate still inputs?
Because nobody publishes them as facts. PPF has a notified rate. NPS is market-linked and the annuity depends on what rates exist when you retire. The honest output is the break-even return NPS would need, not a forecast we invented and called a fact.