Lumpsum Calculator

A lump sum investment is a single amount put in once and left alone. The arithmetic is the plain compound interest formula, and everything interesting about it is in the choice of when to invest rather than in the calculation.

What compounding does over long periods

A = P × (1 + r)ᵗ

On ₹10,00,000 at 12%:

The gap between the first five years and the last five is the point. Years 1 to 5 add ₹7.6 lakh; years 20 to 25 add ₹73.5 lakh, from the same money at the same rate. Nothing accelerates except the base the percentage is applied to.

This is also why the last years of any long plan are the ones worth protecting. Withdrawing in year twenty-two does not cost you three years of growth — it costs you the largest three years.

The rule of 72, and how to use it

Divide 72 by the annual return to get the approximate doubling time. At 12%, money doubles every six years; at 8%, every nine; at 6%, every twelve.

It is a good enough approximation to do in your head, and it makes the effect of a small difference in return visible. Over thirty years, 12% gives five doublings and 8% gives three and a third — a 32× outcome against roughly 10×. A four-point difference in annual return is a threefold difference in the final amount.

Run the same arithmetic on costs. An expense ratio of 1.5% against 0.5% is one point of return, which over thirty years is most of a doubling.

Lump sum or spread it out?

This is the real question, and the honest answer has two halves.

On the evidence, investing it all at once wins more often. Markets spend more time rising than falling, so money held back in cash spends most of its time missing returns. Studies across long periods and several markets find immediate investment beats phased entry roughly two thirds of the time, and the margin grows with the horizon.

Spreading it protects against the third of the time it does not. A lump sum invested a month before a 40% drawdown takes the full hit, and the recovery from that starts from a much lower base. Spreading it over six or twelve months averages the entry price.

The decision is not really about expected return, because the expected return favours investing now and everyone knows it. It is about what you would do if the market fell 30% the week after you invested. If the honest answer is "sell", then spreading the money out is worth more than the return it gives up — because the largest risk to your outcome is not the market, it is the sale.

A reasonable middle course: invest immediately if the horizon is over ten years and the amount is a modest share of your net worth; spread over six to twelve months if it is a windfall large enough to change your life, since that is exactly when a bad start does most psychological damage.

Where lump sums actually come from

The choice usually presents itself for a reason, and the reason matters.

A bonus or maturity proceeds. Predictable, and the sensible default is to invest immediately into the allocation you already hold, because you are not making a market call — you are topping up.

Sale of property or a business. Large, one-off, and often the largest amount the person will ever handle at once. This is where spreading over six to twelve months earns its keep.

An inheritance. Same size profile, plus a reason not to make consequential decisions quickly. Parking it in a liquid fund for three months costs very little and prevents the decisions people regret.

Money that has been sitting in savings. The important observation here is that it is already invested — at 3%, badly. There is no timing question, only a delay that has already cost something.

The assumptions the number rests on

The return is one you chose. Not a projection and not a promise. Indian equity funds have averaged roughly 11–13% over long periods, and that average contains years of +40% and −30%. Run the calculator at 8% and at 12% and treat the pair as the range.

Returns are assumed smooth. They never are, and the order matters more for a lump sum than for a SIP. A bad first year and a bad last year produce the same average and different outcomes, because the loss falls on different amounts of money.

Nothing is withdrawn. A partial withdrawal removes not just the amount but everything it would have earned.

Tax and costs are excluded. Equity gains held over a year attract long-term capital gains tax above the annual exemption; below a year they are taxed at a higher short-term rate. Expense ratios come out of the return before you see it.

Lump sum and SIP are not rivals

They are answers to different questions. A SIP is what you do with income; a lump sum is what you do with capital. Someone with a monthly surplus and an annual bonus should run both, into the same funds, for the same reasons.

The comparison only becomes real when you have a lump sum and are considering converting it into a SIP by drip-feeding it — which is the phased-entry question above, and is the only version of "lump sum against SIP" worth arguing about.

What inflation does to the number

The maturity figure is in future rupees, and future rupees buy less. A projection that ignores this is arithmetically correct and practically misleading.

At 6% inflation, prices roughly double every twelve years. ₹96.46 lakh in twenty years has the purchasing power of about ₹30 lakh today — still three times the ₹10 lakh invested, but not the tenfold gain the headline suggests.

There are two ways to handle it, and mixing them is the common error.

Work in nominal terms throughout. Use a 12% return and then compare the result against the future cost of the goal, inflated at the same rate. A college fee of ₹20 lakh today is roughly ₹64 lakh in twenty years at 6%.

Or work in real terms throughout. Use the real return — approximately the nominal return minus inflation, so about 6% here — and compare against today's prices. The answers agree; what fails is inflating the goal while using a nominal return, or vice versa, which is how people conclude they need either three times too much or a third of what they need.

The real return is what actually matters, and it is smaller and less impressive than every projection implies. It is also the number that explains why a guaranteed 7% deposit is not a substitute for growth assets over long horizons: after tax and inflation it is close to zero.

What this calculator assumes

• A single deposit, compounded at the frequency you select, with nothing added or withdrawn.
• A constant rate across the whole term.
• Figures are before tax, expense ratio and exit load.
• Inflation is not applied, so the maturity figure is in today's rupees only if you set the rate as a real return.
• The term is measured in whole years from the date of investment.