Retirement Corpus Calculator: Monthly Investment to Corpus

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Quick answer

Enter your current age, retirement age, monthly investment and an expected annual return. The tool projects the corpus you could have at retirement and the total you would put in, compounding each monthly contribution at the assumed return. The figure is a gross projection at a constant return and takes no account of inflation, fees or tax. Your figures stay in your browser.

What the Retirement Calculator does

The calculator estimates how big a retirement fund a regular monthly investment could become by the time you stop working. It compounds your contributions at an expected return over the years to retirement and shows the projected corpus next to the total you put in.

Use it to check whether a monthly amount is on track for the fund you want, and how much of the result comes from your own money and how much from growth.

How it works

Your monthly investment is treated as a series of equal contributions. Each one compounds at the assumed return from the month you make it until retirement, and the future-value formula for regular savings adds them up, assuming each payment goes in at the start of the month.

The number of months is the years to retirement times twelve, and the monthly rate is the annual return divided by twelve. Total invested is the monthly amount times the number of months, so the gap between it and the corpus is the projected growth.

Methodology

Find the months and rate. Multiply the years to retirement by twelve, and divide the annual return by twelve for the monthly rate.
Compound each contribution. Grow every monthly contribution at the monthly rate until retirement, assuming start-of-month deposits.
Sum to the corpus. Add the grown contributions to get the projected retirement corpus.
Show the total invested. Multiply the monthly amount by the months to show what you put in.

Retirement corpus (future value)

n = years to retirement × 12 i = annual return ÷ 12 (as a decimal)
corpus = M × ((1 + i)^n − 1) ÷ i × (1 + i) (M = monthly investment)
total invested = M × n

Worked example
age 30 to 60, ₹10,000/month at 10% p.a. → corpus ≈ ₹2.28 crore · invested ₹36 lakh

Returns are constant and deposits go in at the start of each month, the same future-value method a SIP calculator uses. The corpus is in future rupees, with no adjustment for inflation, fees or tax.

Assumptions

The return stays the same every year. Real markets move around from year to year, so the projection is a smooth average and not a guarantee.
Contributions go in at the start of each month and compound monthly until retirement.
The figure is gross and in future rupees. It ignores inflation, so the money will buy less than the same amount today, and it leaves out fees, fund expenses and taxes.

Standards and references

Future value of regular savings: A stream of equal monthly contributions, each compounding until retirement, added up with the standard future-value formula. Paying at the start of each month makes it an annuity-due.
Same method as a SIP: This is the calculation a systematic investment plan (SIP) projection uses: regular contributions compounded at an assumed return. Here the horizon is set by your retirement age.
Gross, not inflation-adjusted: The corpus is in future money. Inflation lowers what it can buy, and fees and taxes reduce the amount you actually get. The projection subtracts none of them.

Accuracy and limits

For the inputs you give, the arithmetic is exact: at a constant return the corpus and the total invested are precise. It shows clearly how much a monthly amount can grow over decades.

The constant return is the big simplification. Real returns rise and fall from year to year and the final corpus depends heavily on that, so treat the figure as a ballpark.

There is no inflation adjustment. A corpus of a couple of crore in thirty years sounds large but will buy far less than it would today, so think about its real value when you judge whether it is enough.

Fees, fund expense ratios and taxes are left out, and each of them lowers the real outcome. Leave a margin, and redo the numbers when your contributions, expected returns or goals change.

Real-world uses

Checking a retirement plan

See whether a monthly amount is on track for your target fund.

Setting a contribution

Find the monthly investment needed for a goal corpus.

Seeing compounding

See how growth overtakes your own contributions over decades.

Comparing start ages

See how starting earlier changes the corpus.

When it fits, and when it doesn't

Good for

Projecting a retirement corpus
Sanity-checking a monthly contribution
Seeing the effect of compounding
Comparing start ages or returns

Not the best choice for

Inflation-adjusted (real) values
Variable or market-realistic returns
Fees, expense ratios and taxes
A guaranteed retirement outcome

For real, inflation-adjusted figures, discount the corpus by expected inflation or use a calculator that does it for you. A tool that models variable returns gives a range instead of a single number. Use this one for a planning estimate.

Frequently asked questions

How does it project the corpus?

It compounds each monthly contribution at the assumed return until retirement and adds them up with the future-value formula for regular savings, assuming start-of-month deposits. Total invested is your monthly amount times the number of months.

Does it account for inflation?

No. The corpus is in future rupees, and those buy less than the same amount today. To judge whether it is enough, think about its value after inflation or discount it by an expected inflation rate.

Is the return realistic?

The tool uses one return for every year, and markets don't behave like that. Actual returns vary, so the projection is a smooth average. Pick a conservative return and treat the result as a ballpark.

Are fees and taxes included?

No, the figure is gross. Fund expense ratios, charges and taxes all reduce what you end up with, so leave a margin and don't read the projected corpus as the amount you will have after costs.

Is this the same as a SIP calculator?

Yes, the maths is the same: regular monthly contributions compounded at an assumed return. This version measures the period up to your retirement age instead of a fixed number of years.

Why does the corpus dwarf what I invested?

Compounding over a long period. Early contributions grow for decades, so most of the corpus is growth. That's why starting early matters so much.

How much should I invest each month?

Change the monthly amount until the projected corpus meets your goal in real terms. The corpus is gross and in future money, so aim above a bare target to allow for inflation, fees and tax.

What return should I assume?

Use a conservative long-run figure for your mix of investments. A lower assumption gives a more cautious plan, and trying a few rates shows you the range.

Does starting earlier really make a big difference?

Yes. Money invested years earlier compounds for longer, so starting even a few years sooner can change the corpus a lot. Try different start ages to see it.

Can I include a lump sum I already have?

The calculator handles regular monthly contributions only. To include money you already have, compound it separately at the same return over the same period and add it to the corpus.

Is my data uploaded?

No. Your browser does the calculation and sends nothing to a server, so your figures stay on your device.

What happens after retirement?

The calculator stops at the corpus on your retirement date and doesn't model spending it. To plan withdrawals, a retirement-income or drawdown calculator estimates how long a corpus lasts at a given spending rate.

References

Monthly contributions, paid at the start of each month, compound at one constant return until retirement age. The result is gross: inflation, fees and tax are not taken out.

SIP Calculator

Estimate what a monthly SIP could grow to: the future value of a regular investment, in rupees, recalculated as you type.