Retirement Calculator: How Much Corpus Do You Need to Retire Comfortably?

"Am I saving enough?" is the wrong question to start with #

Most people ask themselves whether they're saving enough for retirement without ever defining what "enough" actually means in rupees. A retirement corpus calculator flips that around. It starts from your current expenses, adjusts for inflation over however many years you have left to work, and works backward to tell you the exact retirement corpus you'll need and the monthly investment required to build it.

That reframing matters because "save more" is advice nobody can act on directly, while "invest Rs 16,763 a month starting now" is a number you can actually check against your budget.

What a retirement calculator solves for #

A retirement calculator answers two connected questions. First, given your current monthly expenses, your expected retirement age, and inflation, what will your expenses look like by the time you retire, and how large a corpus do you need at that point to sustain them for the rest of your life? Second, given what you've already saved and how many years you have left to invest, how much do you need to put away every month to reach that corpus?

It's different from a SIP calculator or a pure FIRE calculator in one key way: it accounts for what happens after you stop earning, not just how your investments grow while you're still working. The corpus has to survive decades of withdrawals, all while inflation keeps pushing your expenses up.

How the calculation works, step by step #

Step 1: project your expenses forward. Your current monthly expenses grow at the inflation rate every year until you retire.

Monthly expenses at retirement = Current monthly expenses x (1 + inflation rate)^(years to retirement)

Step 2: work out the corpus you need. During retirement, your expenses keep rising with inflation each year, but your remaining corpus also keeps earning a (usually more conservative) post-retirement return. The calculator treats this as the present value of a growing annuity, discounted at the "real" rate, the gap between what your corpus earns and what inflation takes away:

Real rate = (1 + post-retirement return) / (1 + inflation rate) - 1

The required corpus is then this real rate applied to your annual expenses at retirement, spread across your years in retirement.

Step 3: figure out the monthly SIP needed. Given your current savings and the return you expect while still working (usually higher than your post-retirement return, since you can hold more equity), the calculator solves for the monthly investment that closes the gap between what your current savings will grow into and the corpus you actually need.

A worked example #

Take Meena, a 30-year-old marketing manager in Bangalore. She currently spends Rs 50,000 a month, plans to retire at 60, and expects to live until 85. She assumes 6% average inflation, a 12% return on her investments while working, a more conservative 7% return during retirement, and she already has Rs 5,00,000 saved specifically for retirement.

Step 1: Over 30 years at 6% inflation, her monthly expenses of Rs 50,000 grow to roughly Rs 2,87,175 by the time she turns 60. That's not a typo. Inflation compounding over three decades roughly quintuples what "comfortable" costs.

Step 2: With a post-retirement return of 7% against 6% inflation, her real rate works out to under 1%, which means her corpus has to do most of the heavy lifting itself rather than relying much on returns to outpace her rising expenses over 25 years in retirement. The required corpus comes out to approximately Rs 7,71,48,478, just over 7.7 crore.

Step 3: Given her existing Rs 5,00,000 and 30 years to invest at 12%, Meena needs to invest roughly Rs 16,763 every month from now until she retires to hit that corpus.

You can run this exact scenario on the retirement calculator and see the year-by-year accumulation. If Rs 16,763 a month feels steep against her current budget, the calculator also shows what happens if she pushes her retirement age to 62 or trims her expected post-retirement expenses, both of which reduce the required monthly SIP.

Why the corpus number is always bigger than people expect #

Inflation compounds over decades, not years. A 6% inflation rate feels manageable year to year, but stretched across 30 years it multiplies your expenses by more than 5x. Most people underestimate this because they're used to thinking about inflation in single-digit, single-year terms.

Retirement itself can last 25 to 30 years. With rising life expectancy, a corpus built for a 60-year-old might need to last until 85 or 90. That's nearly as long as the accumulation phase itself, and every one of those years still needs inflation-adjusted withdrawals.

Post-retirement returns are deliberately conservative. Once you're withdrawing from the corpus, most planners recommend shifting toward debt and away from equity to reduce volatility. That lower return means the corpus has less help compounding, so it needs to start bigger.

Common mistakes people make when estimating their retirement number #

Using today's expenses as the retirement target, unadjusted for inflation. Someone assuming they'll need "Rs 50,000 a month" in today's rupees at age 60 is understating their actual need by nearly 6x if inflation runs at 6% for 30 years, exactly as Meena's example shows.

Ignoring healthcare costs, which inflate faster than general expenses. Medical inflation in India has historically outpaced general inflation. A retirement plan that uses a single blended inflation rate for everything, including healthcare, is likely underestimating the corpus needed for the later retirement years.

Assuming the same return rate before and after retirement. It's tempting to run the whole projection at one optimistic rate, say 12%, throughout. In practice, most people reduce equity exposure after retirement to manage sequence-of-returns risk, which lowers the realistic post-retirement return and increases the required corpus.

Treating the required monthly SIP as fixed forever. The number a retirement calculator gives you today assumes a static monthly contribution. In reality, most people increase their contribution as their salary grows. A step-up approach, even a modest 5-10% annual increase, can meaningfully reduce the burden in your final working years compared to a flat contribution.

Tips for building toward your number #

• Recalculate every two to three years, or whenever your expenses change meaningfully (a new home loan, a child, a job change), since the required corpus and SIP shift with your actual life, not a projection made years ago.
• Use a SIP calculator alongside the retirement calculator to check whether spreading the required monthly investment across equity mutual funds at your target return is realistic given your current portfolio. A Rs 10,000 monthly, 15-year SIP example is a useful reference point to compare your own numbers against.
• If you're a salaried employee, treat your EPF calculator projection as one input toward your total retirement corpus, not the whole answer. EPF alone rarely covers the full number a retirement calculator produces.
• Consider NPS as a second retirement vehicle. Check the projected pension using an NPS calculator and layer it against the withdrawal plan for your other retirement savings.
• Don't wait for a "round number" salary or milestone to start. Every year you delay pushes more of the required corpus onto fewer remaining years of compounding.

Frequently asked questions #

How is a retirement calculator different from a FIRE calculator? #

A FIRE calculator typically works forward from your current savings rate to tell you when you could retire, often assuming an aggressive early retirement timeline. A retirement calculator works backward from a target retirement age and life expectancy to size the corpus and required monthly investment. Both are useful, but they answer different questions: "when can I stop working" versus "how much do I need for the retirement age I've already chosen."

What inflation rate should I use? #

There's no single correct number, but 6% is a commonly used long-term assumption for India, roughly matching the historical average consumer price inflation over the past couple of decades. If you want to be conservative, running the numbers again at 7% gives you a sense of how much cushion you'd need if inflation runs hotter than expected.

Should I include my current EPF and PPF balances in the calculator's "current savings" input? #

Yes, if they're earmarked for retirement rather than for a nearer-term goal like a house down payment. The current savings figure should represent money you genuinely don't plan to touch before retirement age.

Is 25 to 30 years a reasonable estimate for how long my corpus needs to last? #

It depends on your retirement age and family longevity. If you plan to retire at 60 and have reason to expect a long lifespan (family history, current health), planning for the corpus to last until 85 or even 90 is a safer assumption than a shorter horizon. Running the calculator at two different life expectancy assumptions shows you how sensitive your required corpus is to this one variable.

Find your number #

The gap between vague retirement anxiety and an actual plan is one calculation. Open the retirement calculator, enter your real expenses, age, and return assumptions, and see the corpus and monthly SIP the math actually requires. Whatever the number turns out to be, it's easier to work toward a specific target than to keep saving "as much as feels reasonable" and hoping it adds up.