Investor education
SIP vs Lump Sum: What the Numbers Actually Show
A balanced look at SIP vs lump sum investing: how rupee-cost averaging works in arithmetic, why outcomes depend on the period, and how to compare the two fairly.
IntelliWealthPro Team· Research desk· · 5 min read
Key takeaways
- A SIP spreads purchases over time; a lump sum invests everything at once.
- Rupee-cost averaging lowers the average cost relative to the average NAV, but does not decide which method ends ahead.
- In periods when markets rise, money invested earlier has longer exposure; in volatile or falling periods, spreading can help.
- STP is a middle path for someone who already holds a lump sum.
- Compare outcomes with XIRR and use periods from official factsheets, remembering past performance may or may not be sustained.
On this page
SIP vs lump sum is one of the most common questions mutual fund investors ask. The honest answer is that neither method wins in every period. What each method does is different, and the numbers below show how. Everything here is arithmetic, not a forecast.
What each method means
- SIP (Systematic Investment Plan): a fixed amount, say ₹10,000, is invested at regular intervals, usually monthly. Units are bought at whatever the NAV is on each date.
- Lump sum: the whole amount, say ₹50,000, is invested on one day at that day's NAV.
Most salaried investors earn monthly, so a SIP often matches how money actually arrives. A lump sum usually comes from a bonus, a maturity, a property sale or savings already in the bank.
Rupee-cost averaging, in arithmetic
The illustration below uses a hypothetical scheme over five months. These NAVs are invented for the example. They are not a forecast and not based on any real scheme.
Example 1: a market that dips and recovers
₹10,000 invested each month by SIP:
| Month | NAV (₹) | Amount (₹) | Units bought |
|---|---|---|---|
| 1 | 100 | 10,000 | 100.000 |
| 2 | 80 | 10,000 | 125.000 |
| 3 | 90 | 10,000 | 111.111 |
| 4 | 110 | 10,000 | 90.909 |
| 5 | 120 | 10,000 | 83.333 |
| Total | 50,000 | 510.354 |
- Average cost per unit: ₹50,000 / 510.354 = ₹97.97
- Simple average of the five NAVs: (100 + 80 + 90 + 110 + 120) / 5 = ₹100.00
- Value at month 5 NAV of ₹120: 510.354 x 120 = ₹61,242.42
Lump sum of ₹50,000 at NAV ₹100 in month 1:
- Units: 500.000
- Value at ₹120: ₹60,000.00
In this example the SIP ends slightly ahead, because it bought extra units during the dip in months 2 and 3.
Example 2: a market that rises steadily
Now the same ₹10,000 a month with NAVs of 100, 105, 110, 115 and 120:
- SIP units: 100.000 + 95.238 + 90.909 + 86.957 + 83.333 = 456.437
- Average cost: ₹50,000 / 456.437 = ₹109.54
- Value at ₹120: ₹54,772.44
- Lump sum: 500 units at ₹100, worth ₹60,000.00
Here the lump sum ends ahead, because all of it was invested before the rise.
What the two examples show
Rupee-cost averaging always makes the average cost per unit at most equal to the simple average NAV on purchase dates. It does not decide which method ends with more money. That depends on the path the market takes.
The general reasoning
There is a simple logic behind the two examples.
- When markets rise over a period, money invested earlier is exposed to that rise for longer. A lump sum is fully invested from day one, so in rising periods it has often ended ahead.
- When markets are volatile or fall after you invest, spreading purchases reduces the risk of putting everything in at a high point. A SIP also reduces regret: you never have to decide whether today is the right day.
This is reasoning, not a statistic. Historical outcomes depend heavily on the start and end dates chosen, and past performance may or may not be sustained in future.
STP: a middle path for a lump sum
If you already have a lump sum but are uneasy about investing it in one go, a Systematic Transfer Plan (STP) is one option. The money is first placed in a scheme such as a liquid or debt fund, and a fixed amount is transferred to another scheme of the same AMC at regular intervals.
Points to check in the scheme documents:
- Exit load, if any, on the source scheme
- Tax on each transfer, since every transfer is a redemption from the source scheme
- Minimum transfer amounts and frequency allowed
Behaviour matters as much as method
The method you can stick with often matters more than the method on paper.
- Staying invested. Many investors stop SIPs after a market fall, which is exactly when SIPs buy more units.
- Pausing SIPs. Some AMCs allow a SIP pause. If cash flow is tight, a pause may be more practical than cancelling, but read the terms.
- Lump sum anxiety. An investor who invests a large amount and then watches it fall 15% may redeem at the wrong time. Knowing your own reaction in advance is useful.
How to compare the two fairly
Absolute return can mislead, because each SIP instalment was invested for a different length of time. Use XIRR, which accounts for the date and size of every cash flow. Our guide on how to calculate XIRR for a mutual fund SIP walks through the method in a spreadsheet.
When looking at history, use rolling returns over many start dates rather than one chosen period, and take data from official AMC factsheets or AMFI.
What your MFD can show you
A mutual fund distributor can help you understand both methods without recommending one:
- The arithmetic, like the examples above, using hypothetical numbers
- Past rolling-return data from official factsheets, with the period clearly stated
- How an STP would work mechanically, including tax and exit load
- Your past SIP and lump sum investments, measured with XIRR
Questions worth asking yourself
- Do I have the full amount now, or will it come in monthly from salary or business income?
- How would I feel if the value fell sharply soon after investing a large amount?
- How long can this money stay invested without being needed?
- Will I keep a SIP running through a market fall?
The decision itself depends on your cash flows, risk profile and investment horizon. Read all scheme-related documents before deciding.
Information only. Not investment advice. Mutual fund investments are subject to market risks; read all scheme-related documents carefully.
Frequently asked questions
Does a SIP always give a lower average cost?
A SIP buys more units when NAV is lower and fewer when it is higher, so its average cost per unit is never above the simple average of the NAVs on purchase dates. That does not mean it will end ahead of a lump sum; that depends on how the market moves.
Which one should I choose?
There is no single answer. It depends on whether you have the money now or earn it monthly, your risk profile, your horizon and how you would react to a fall. Read the scheme documents and consider your own circumstances.
What is an STP?
A Systematic Transfer Plan moves a fixed amount at regular intervals from one scheme, often a debt or liquid scheme, to another scheme of the same AMC. It lets a lump sum enter equity gradually.
How should I compare a SIP with a lump sum?
Use XIRR, which accounts for the timing of each cash flow. Absolute return alone makes a SIP look worse or better than it is because each instalment was invested for a different length of time.
Mutual fund investments are subject to market risks; read all scheme-related documents carefully. This article is general information for mutual fund distributors and their clients. It is not investment, tax or legal advice and not a recommendation to buy, sell or hold any scheme. Past performance does not indicate future returns.