Goal-Based SIPs: The Arithmetic
Linking a SIP to a goal is a two-step estimate: an assumed inflation rate turns today's cost into a future cost, and an assumed rate of return turns that cost into a monthly instalment. This lesson shows both steps and why the answer is an estimate.
Four inputs
A goal calculation needs four things: a target amount, a date, an assumed inflation rate and an assumed rate of return. The first two describe the goal. The last two are assumptions chosen for the calculation, not forecasts.
Step one: from today's cost to a future cost
Prices rise over time, so the amount needed on the goal date is usually more than the cost today. The estimate is: future cost = today's cost × (1 + assumed inflation rate)^years.
The rate compounds. Adding the same percentage of today's cost for each year understates the result, because each year's rise is worked out on the previous year's higher cost. For reference, all-items consumer price inflation was 4.82% in August 2026 (MoSPI). That is a measured figure for a broad basket of goods and services; the rate used in a goal calculation is an assumption, and the cost of a particular goal can rise faster or slower.
Step two: from a future cost to a monthly instalment
The second step asks what monthly instalment might grow to the target. Monthly instalment needed = target amount ÷ the future value of ₹1 a month at the assumed rate.
The future value of ₹1 a month depends on the convention, which has to be stated: the rate per month, and whether instalments are paid at the start or the end of each month. At an assumed 0.5% a month with end-of-month instalments, ₹1 a month grows to ₹163.88 over 120 months.
An estimate to revisit, not a promise
The result is an estimate. A scheme's returns are not assured, and the value of the units on the goal date can be above or below the figure worked out. If actual returns are lower than assumed, the same instalment falls short. The estimate is therefore revisited as costs and values change.
Some investors move money from equity schemes to debt schemes as a goal nears. This lowers exposure to share prices, but debt schemes carry interest-rate and credit risk and do not guarantee capital. No rule requires such a move. Each transfer, including one made through an STP, is a redemption from the equity scheme, so capital-gains tax and any exit load can apply.
Rules at a glance
A course fourteen years away (illustrative)
A course costs ₹15,00,000 today, and Deepa wants an estimate of its cost in 14 years. She assumes, for the arithmetic only, that the cost rises by 6% a year. Since (1.06)^14 = 2.2609, the estimated future cost is 15,00,000 × 2.2609 = ₹33,91,350, about ₹33.91 lakh.
Adding 6% of today's cost for each of the 14 years would give 15,00,000 × 1.84 = ₹27,60,000, which is ₹6,31,350 lower because it ignores compounding. The 6% is an assumption, not a measured or expected rate of inflation.
Instalment for a target of ₹30,00,000 in 10 years (illustrative)
- Assumptions, for arithmetic only: growth of 0.5% a month, with instalments at the end of each month. On these assumptions ₹1 a month grows to ₹163.88 over 120 months.
- Instalment = target ÷ future value of ₹1 a month = 30,00,000 ÷ 163.88 = about ₹18,306.
- Amount paid in = 18,306 × 120 = ₹21,96,720. The remaining ₹8,03,280 of the target is assumed growth.
- With no growth at all, the instalment would be 30,00,000 ÷ 120 = ₹25,000 a month.
- With instalments at the start of each month instead, the factor is 163.88 × 1.005 = about 164.70, and the instalment is 30,00,000 ÷ 164.70 = about ₹18,215.
Result. About ₹18,306 a month reaches ₹30,00,000 on the stated assumptions. If actual growth is lower than 0.5% a month the same instalment falls short: with no growth it would reach only ₹21,96,720.
Key points
- A goal calculation needs a target amount, a date, an assumed inflation rate and an assumed rate of return.
- Future cost = today's cost × (1 + assumed inflation rate)^years.
- Monthly instalment needed = target amount ÷ the future value of ₹1 a month at the assumed rate, with the convention stated.
- Both rates are assumptions, so the result is an estimate to be revisited, not a promise.
- Moving from equity to debt schemes near a goal lowers equity exposure, but each transfer is a redemption and debt schemes can also fall in value.
Common misunderstandings
- The assumed rate of return is not a forecast: a scheme's returns are not assured, and the value on the goal date can be below the estimate.
- Future cost is not today's cost plus a flat percentage for each year: the assumed rate compounds, so the simple sum understates it.
- A debt scheme is not a guaranteed resting place near a goal: debt schemes carry interest-rate and credit risk and can also fall in value.
Questions people ask
Why are two different rates needed?
One estimates how the cost of the goal grows (an assumed inflation rate). The other estimates how the instalments grow (an assumed rate of return). They are separate assumptions.
What happens if the actual return is lower than the assumed rate?
The same instalment reaches less than the target. That is why the result is an estimate to be revisited.
Is there a rule that money must move to debt schemes before a goal?
No. Some investors do so to lower equity exposure, but no rule requires it, and each transfer is a redemption.
What this lesson relies on
- Ministry of Statistics and Programme Implementation (MoSPI), consumer price index release of 14 September 2026 (inflation for August 2026)
- Income-tax Act, 2025 (capital gains on redemption of units)
This lesson was reviewed independently against these sources on 8 October 2026. Rules change: check the current regulation, scheme document or policy wording before relying on any figure. This is education, not advice.