How to Work Out the SIP You Need for a Goal
The short answer
Work out the SIP for a goal in four steps: grow today's cost to what it will cost on the goal date using an inflation assumption, work out what money you have already set aside will grow to, subtract that from the target to find the gap, then invert the SIP formula to find the monthly amount that closes the gap over your time period. The answer is only as good as the two assumptions you chose — the inflation rate and the return rate — so treat it as a starting range, not a precise figure.
"How much SIP do I need?" is the most practical question in personal investing, and it has an actual answer. It is arithmetic, not opinion.
What makes it useful is doing it in the right order, and being honest about the two numbers you had to assume along the way.
Step 1: Work out what the goal will cost, not what it costs
Almost every goal costs more on the day you need it than it does today. A course that costs ₹20 lakh now will not cost ₹20 lakh in twelve years, and planning towards today's figure quietly guarantees a shortfall.
Grow today's cost at an inflation rate you choose for that specific goal. General living costs, education costs and property prices have not historically risen at the same rate, so a single number applied to everything is a simplification you should be aware you are making.
Step 2: Credit what you have already set aside
Money already earmarked for this goal keeps compounding while you invest. Ignoring it makes the required monthly amount look larger than it is.
Grow that existing amount to the goal date at the return you are assuming, and subtract it from the target. Be strict about what counts: money genuinely earmarked for this goal, not your emergency fund and not the same savings you have already mentally allocated to a different goal.
Step 3: Find the gap
The target minus what your existing savings grow to is the gap — the amount your future monthly investing actually has to produce.
If the gap is zero or negative, the arithmetic says the goal is already covered under these assumptions. That is a statement about your assumptions, not a guarantee.
Step 4: Invert the SIP formula
A SIP calculator normally goes forwards: given a monthly amount, a rate and a period, it produces a future value. Here you need it backwards: given a future value, a rate and a period, what monthly amount gets there?
That is exactly what a required-SIP calculation does. The output is a single monthly figure — and it is worth computing it at more than one assumed return, because the answer moves a great deal with that assumption.
Why you should compute it at several rates
The required monthly amount is highly sensitive to the return you assume. Running the same goal at 8%, 10% and 12% shows you a range rather than one number that looks like a promise.
If the goal only works at the most optimistic rate, the arithmetic is telling you something useful: the plan has no margin. That is a reason to extend the period, raise the contribution, or revise the target — not a reason to assume a higher return.
When the required amount is more than you can invest
This is common, and it is not a failure of the method. You have four honest levers: invest more, give the goal more time, reduce the target, or accept a partial outcome and fund the rest another way.
There is a fifth lever people reach for — assuming a higher return — and it is the only one that changes nothing in the real world. Markets do not deliver more because a spreadsheet needed them to.
What this arithmetic cannot know
It does not know your income, your loans, your other goals or your emergency fund, so a monthly figure that is arithmetically correct can still be wrong for your situation.
It also assumes a constant rate every year, no withdrawals, and figures before tax and charges. Real returns arrive unevenly, and the order in which good and bad years land changes the outcome — especially near the end of the period, when the balance is largest.
Key takeaways
- Inflate today's cost to the goal date before doing anything else.
- Credit what you have already set aside — ignoring it overstates the monthly amount.
- The gap, not the target, is what your future SIP has to produce.
- Compute the required amount at several assumed rates to see a range instead of one number.
- If the goal only works at the most optimistic rate, the plan has no margin.
- Assuming a higher return is the one lever that changes nothing in reality.
Put this to work on your own numbers
- Required SIP Calculator
Do step 4 directly: enter a target, a rate and a period, and get the monthly amount.
- Goal Planner
Run all four steps in order for a specific goal, at three assumed rates at once.
- Inflation Calculator
Do step 1 on its own: grow today's cost to the goal date.
- Child Education Calculator
The same four steps, pre-arranged for an education goal.
For illustration only. Not investment advice. Mutual fund investments are subject to market risks; read all scheme related documents carefully. Returns assumed are hypothetical and not guaranteed.
Frequently asked questions
Sources and editorial review
Checked against the primary sources below on . Scheme terms, tax rules and regulatory requirements change — confirm the current position before acting on anything here.
- SEBI Investor Website
SEBI's investor education material on goal-based investing and the limits of return assumptions.
- AMFI Investor Corner
AMFI's investor education material on systematic investing.
- MutualFundAdvisor.in editorial policy
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Amit Chadha is a Mutual Fund Distributor (ARN: 349461). The first conversation is free and educational.