What the NPS calculator projects
The calculator estimates your total NPS corpus at retirement based on your monthly contribution, an assumed annual return, and your current and retirement age, then splits that final corpus into two pieces: the portion you can withdraw as a tax-free lumpsum, and the portion that must be annuitised — used to purchase a pension plan — based on the annuity percentage you select.
This split is the single most important thing the calculator shows beyond the headline corpus figure, because these two portions behave completely differently after retirement. The lumpsum is money you receive and control outright. The annuitised portion is converted into a completely different financial product — a monthly pension — and stops being a lump sum you can access or reinvest.
Why the annuity portion isn't really part of your "corpus" anymore
It's tempting to look at the total corpus figure and think of it as your retirement wealth, the way you might think of an EPF or PPF balance. But the minimum 40% that must go into an annuity converts into a fixed income stream, priced at whatever the annuity rate happens to be when you retire — not the return rate you assumed while contributing.
This matters because annuity rates have historically been modest, often in the 5–7% range, well below what the same money might have earned if you could have kept it invested and growing instead. The calculator's separate annuity rate input reflects this reality — it deliberately doesn't assume your NPS growth rate continues into the annuity phase, because it doesn't.
A worked example showing the split
Take a 30-year-old contributing ₹5,000 a month until age 60, assuming a 10% annual return with the minimum 40% annuitisation. Over 30 years, this produces a corpus in the ₹1.1–1.2 crore range. Of that, roughly ₹66–72 lakh becomes available as a tax-free lumpsum, while the remaining ₹44–48 lakh is annuitised.
At a 6.5% annuity rate, that annuitised portion generates an estimated monthly pension in the rough range of ₹24,000–26,000 — a fixed, taxable income for life, but one that doesn't grow with inflation unless you specifically choose an inflation-indexed annuity product, which typically starts at a lower initial payout in exchange for that protection.
Why the annuity percentage slider matters more than it looks
The calculator lets you increase the annuitised share above the 40% minimum, up to 100%. Raising this reduces your lumpsum and increases your locked-in pension income, which is a genuine trade-off between liquidity now and guaranteed income for life — not a strictly better or worse choice, but one that depends heavily on what other retirement assets you already have.
If EPF, PPF, or other investments already give you a solid lumpsum-accessible retirement corpus, annuitising close to the 40% minimum and keeping more of your NPS as lumpsum may make sense. If NPS is a larger share of your total retirement planning, a higher annuity percentage builds more guaranteed monthly income, at the cost of locking away more capital permanently.
How the equity/debt mix inside NPS affects your return assumption
NPS lets you choose an asset allocation across equity, corporate bonds, and government securities, either through active choice or an auto-allocation model that shifts toward safer assets as you approach retirement. The calculator's single return-rate input is a simplification of whatever blended return this mix actually produces over your contribution period.
A younger investor with a higher equity allocation might reasonably assume a return closer to 10–12%, while someone closer to retirement with an auto-allocation model shifting toward bonds should assume something more conservative, closer to 7–9%, for the years nearer retirement even if earlier years ran higher.
Common mistakes when using an NPS calculator
Treating the full corpus as spendable. The annuitised portion isn't accessible as a lump sum — it's already been converted into a pension income stream, which is a different kind of asset with different liquidity.
Assuming today's annuity rate holds for 20–30 years. Annuity rates at the time you actually retire could be meaningfully different from what the calculator assumes today, since they depend on interest rate conditions decades from now.
Ignoring that pension income is taxable. Unlike the tax-free lumpsum, the monthly annuity pension is taxed as regular income in the year you receive it — factor this into how much net monthly income the annuity portion actually delivers.