Goal Arithmetic: an Illustration
A financial goal can be turned into a number with simple arithmetic. This lesson shows how an assumed inflation rate gives a future cost, how the same arithmetic run backwards gives an amount needed today, and why every result is an illustration.
From today's cost to a future cost
Prices compound: each year's rise is applied to the previous year's higher price. So the estimated future cost of something is today's cost multiplied by (1 + inflation rate) once for each year: future cost = today's cost × (1 + rate)^years. The figure (1 + rate)^years is called the growth factor.
Multiplying the rate by the number of years and adding it on is simple interest. It ignores compounding and understates the result, and the shortfall widens as the period lengthens.
The rate is an assumption
The inflation rate in the formula is an assumption, not a forecast. For reference, all-items consumer price inflation was 4.82% for August 2026 (MoSPI release of 14 September 2026). Past inflation does not fix future inflation, and the cost of a particular goal can rise faster or slower than the general index.
A small change in the assumed rate changes the answer a good deal over long periods. That is why an illustration always states the rate it used and calls it an assumption.
Running the arithmetic backwards
The same arithmetic shows how much would be needed today under a given growth assumption: amount needed today = future cost ÷ growth factor at the assumed rate of growth. Dividing gives a present value; multiplying would run the calculation the wrong way.
The rate of growth is again an assumption. Returns on market-linked investments are not assured, and actual growth may be higher, lower or negative.
Illustration, not a plan
These calculations show how the numbers behave. They are not a plan for any person. Under the SEBI (Investment Advisers) Regulations, 2013, investment advice includes financial planning, so preparing a personal financial plan is the work of a SEBI-registered investment adviser.
Rules at a glance
Compound and simple arithmetic compared (illustrative)
A course costs ₹25 lakh today. Assume, for illustration only, that its cost rises by 6% a year for 12 years; the growth factor (1.06)^12 is 2.012. Estimated future cost = 25 × 2.012 = ₹50.30 lakh.
Simple interest would add 6% × 12 = 72% to today's cost, giving 25 × 1.72 = ₹43.00 lakh. The compound figure is ₹7.30 lakh higher. The 6% is an assumed rate for the illustration, not a measure or forecast of actual inflation.
Two inflation assumptions, then a present value (illustrative)
- A goal costs ₹8,00,000 today and is 10 years away. The growth factor for 10 years is 1.629 at an assumed 5% a year and 1.967 at an assumed 7% a year.
- At 5%: 8,00,000 × 1.629 = ₹13,03,200.
- At 7%: 8,00,000 × 1.967 = ₹15,73,600.
- Difference between the two assumptions: 15,73,600 − 13,03,200 = ₹2,70,400.
- Now run the arithmetic backwards for the 7% estimate. Assume, not as a forecast, that money set aside today grows at 8% a year; the growth factor for 10 years is 2.159.
- Amount needed today = 15,73,600 ÷ 2.159 = about ₹7,28,856, or about ₹7.29 lakh.
Result. A two-point change in the assumed inflation rate moves the estimate by ₹2,70,400. On the 7% and 8% assumptions, about ₹7.29 lakh today corresponds to ₹15,73,600 in 10 years; actual growth may be higher, lower or negative.
Key points
- Future cost = today's cost × (1 + assumed inflation rate)^years.
- The rate used is an assumption; a different rate gives a different answer, and the gap grows with time.
- Amount needed today = future cost ÷ growth factor at the assumed rate of growth.
- Simple interest ignores compounding and understates a future cost.
- Illustrations are not forecasts; returns on market-linked investments are not assured.
Common misunderstandings
- The inflation rate in a goal calculation is not a forecast: it is an assumption, and a different rate gives a different answer.
- Future cost is not today's cost plus rate × years: that is simple interest, which ignores compounding.
- Dividing by the growth factor gives the amount needed today, not the future cost: multiplying runs the arithmetic the wrong way.
Questions people ask
Is the latest published inflation figure the right rate to use?
It is a reference point only. Past inflation does not fix future inflation, so whatever rate is used remains an assumption.
Why does the assumed rate matter so much?
Because it compounds. Over 10 years, moving the assumption from 5% to 7% raises the growth factor from 1.629 to 1.967, about a fifth more.
Who may prepare a personal financial plan?
A SEBI-registered investment adviser. Financial planning is part of investment advice under the SEBI (Investment Advisers) Regulations, 2013.
What this lesson relies on
- Ministry of Statistics and Programme Implementation (MoSPI), consumer price index release of 14 September 2026 (inflation for August 2026)
- SEBI (Investment Advisers) Regulations, 2013
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.