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A systematic investment plan (SIP) and a lump-sum investment are two ways of putting money into a fund that has already been chosen. They are not two different products. The fund, the category and the time horizon remain the same. What changes is whether money enters once or in instalments. For most salaried households, the SIP is the practical default. A lump sum is appropriate when a large amount is already available and the horizon is long enough to absorb an unlucky starting date.
A SIP instructs the bank or platform to invest a fixed amount on a stated date — for example ₹10,000 on the fifth of every month — into a chosen scheme. Units are allotted at that day’s NAV. In a month when the NAV is lower, the same rupee amount buys more units. In a month when the NAV is higher, it buys fewer units. Over a full cycle this is called rupee-cost averaging. It is a mechanical effect. It is not a promise that the average purchase price will beat every lump-sum investor.
The larger benefit for most people is behavioural. Salary arrives monthly. A SIP uses that rhythm. It removes the need to decide, each month, whether the market “looks right.” That decision is the point at which many intended investments never leave the savings account.
A lump sum is simply a one-time purchase of units. It is reasonable when:
There is no reliable method, available to a household, for identifying the single best day. Waiting indefinitely for that day is itself a decision: the money remains in cash and misses the years it was meant to work.
A systematic transfer plan (STP) places the lump sum first in a liquid or ultra-short debt fund and then moves a fixed amount each month into the equity fund. The cash earns a modest return while it waits. The equity fund is entered in instalments. This is useful when a large amount has arrived and the investor does not wish to commit it to equity on one day. It is unnecessary when the household is simply investing from monthly surplus; a SIP is then sufficient.
Suppose ₹1.2 lakh is to be invested in a diversified equity fund over a year.
| Method | What happens |
|---|---|
| SIP of ₹10,000 a month | Twelve purchases at twelve NAVs. More units in weaker months. |
| Lump sum of ₹1.2 lakh on day one | One purchase at one NAV. If markets rise immediately, this can look better. If they fall, the entire amount participates in the decline from the first day. |
| STP from liquid to equity | The ₹1.2 lakh sits in a liquid fund and moves across in twelve parts. |
No table can tell you which path will produce the higher value in the next twelve months. Over a decade, the difference between a SIP and a well-timed lump sum is often smaller than the difference between continuing the plan and stopping it.
The most common failure is not choosing SIP instead of lump sum. It is starting a SIP and pausing it when the account shows a decline. That decision converts rupee-cost averaging from an advantage into a missed opportunity: the months with lower NAVs are the months that are skipped. If cash flow is genuinely under strain, reducing the amount is more sensible than stopping altogether and promising to “restart at a better level.”
Each SIP instalment is a separate purchase for tax purposes. The holding period of the January instalment is not the same as that of the December instalment. Article 6 returns to this point.
Tarun, who works in Hubballi, received a bonus of ₹3 lakh and spent six weeks waiting for the index to “correct.” It did not. He then placed the amount in a liquid fund and began an STP of ₹25,000 a month into the same flexi-cap fund in which he already ran a SIP from salary. He did not attempt to choose a single day. He also did not leave ₹3 lakh in a current account for a year. The bonus entered the long-term holding in twelve steps; the salary SIP continued as before.
For monthly surplus, a SIP is the natural method. For money that has already arrived, a lump sum or an STP is a choice about starting-date risk, not a choice about which fund to own.
Stopping a SIP after three weak months in order to “wait for stability,” and then never restarting it on a schedule. Stability, in equity markets, is recognised after it has passed.