How a SIP grows: the formula, step-up SIPs and the SIP Calculator
AdvertisementA Systematic Investment Plan, or SIP, is a simple habit: invest a fixed amount every month instead of waiting for a perfect moment to invest a large sum. People use SIPs to buy mutual funds, and the idea is to build wealth slowly through regular contributions and compounding. The question everyone asks is the same: "If I put in this much each month, what could it become?" The free SIP Calculator gives an estimate, with an optional yearly step-up and a year-by-year table. This guide explains what the estimate means, how it is calculated and, just as important, what it can never tell you.
What a SIP does
Each month a fixed amount leaves your bank account and buys units of a fund at that day's price. When the price is high you get fewer units, when it is low you get more. This is sometimes called rupee-cost averaging: over time your average buying price tends to smooth out. It does not remove risk, and it does not guarantee profit, but it removes the pressure of timing the market and builds the discipline of investing regularly.
The reason a SIP can grow into a large number is compounding: the returns you earn are reinvested and start earning returns of their own. Compounding is slow at first and fast later, so the length of time matters more than almost anything else.
The estimate behind the calculator
The tool assumes that each instalment is invested at the start of the month and grows at a monthly rate equal to the yearly return divided by 12. Without a step-up the value after n months is:
Value = M × ((1 + i)ⁿ − 1) ÷ i × (1 + i)
where M is the monthly amount, i is the monthly rate (yearly rate ÷ 12 ÷ 100) and n is the number of months. This is a standard formula for a series of equal payments that each earn the same rate. Real funds do not grow at a smooth rate; their value moves up and down every day. The calculator is therefore an illustration of an assumed constant return, not a prediction.
A worked example
A monthly SIP of ₹10,000 for 10 years with an assumed return of 12% a year:
- Total invested: ₹10,000 × 120 months = ₹12,00,000
- Estimated value: about ₹23,23,391
- Estimated gain: about ₹11,23,391
So almost half of the final amount is the growth you did not have to put in. Now see what time does with the same ₹5,000 a month at 12%:
| Years | Invested | Estimated value | Gain |
|---|---|---|---|
| 10 | ₹6,00,000 | ₹11,61,695 | ₹5,61,695 |
| 15 | ₹9,00,000 | ₹25,22,880 | ₹16,22,880 |
| 20 | ₹12,00,000 | ₹49,95,740 | ₹37,95,740 |
Going from 15 to 20 years adds only ₹3,00,000 of your own money but about ₹24 lakh to the estimated value. The last years of a long SIP do most of the work. That is the practical reason to start early, even with a small amount.
The step-up: raising the SIP every year
Most people's income grows, so a SIP that stays at the same amount slowly shrinks in importance. A step-up SIP raises the instalment by a fixed percentage once a year. The calculator has a step-up box for this.
Take the same ₹10,000 SIP at 12% for 10 years, with a 10% yearly step-up (₹10,000 in year one, ₹11,000 in year two, and so on):
| Plan | Invested | Estimated value |
|---|---|---|
| Flat ₹10,000 | ₹12,00,000 | ₹23,23,391 |
| 10% yearly step-up | ₹19,12,491 | ₹33,74,326 |
You invest about ₹7 lakh more, spread over ten years, and the estimated value is over ₹10 lakh higher. A step-up is one of the most effective ways to improve the result because the bigger, later instalments still have years to compound. Match the step-up to what your income realistically does.
The effect of the return rate
The assumed return changes the answer a lot. For ₹10,000 a month over 10 years:
| Assumed return | Estimated value |
|---|---|
| 8% | ₹18,41,657 |
| 12% | ₹23,23,391 |
Nobody knows what return a fund will deliver. Equity funds have long periods of strong growth and long periods of little, and some years lose money. So use the calculator in a sensible way: try a conservative rate, an optimistic one, and a low one, and plan around the range, not the best number. If your goal only works at a very high return, change the plan (a larger SIP, a longer period or a lower goal), not the assumption.
Using the calculator
- Open the SIP Calculator.
- Enter your monthly investment, the expected yearly return and the number of years.
- Optionally enter a yearly step-up percentage.
- Compare the amount invested with the estimated value and the gain.
- Read the year-by-year table to see how the value grows, and notice how much of it arrives in the last years.
Everything is calculated in your browser, and nothing you type is stored.
What the estimate leaves out
- Costs. Funds charge an expense ratio that reduces returns, so enter a return that is already net of costs for a closer estimate.
- Taxes. Capital-gains tax applies when you sell units, so the amount you keep is lower.
- Inflation. ₹23 lakh in ten years buys less than ₹23 lakh today. If prices rise 6% a year, the buying power of that amount is much smaller. Compare your goal in future prices.
- Market ups and downs. Real returns are uneven. A SIP started just before a long fall looks bad for a while.
- Missed instalments. Pausing even for a few months reduces the result.
SIP, lump sum or loan?
A SIP suits regular income and long goals such as retirement, a child's education or a house deposit. A lump sum suits money you already have and can leave alone; see how it grows with the Compound Interest Calculator. If you also have a loan, compare what the loan costs in the EMI Calculator with what an investment might earn: paying off an expensive loan early is often a guaranteed "return" equal to its interest rate, which is not true for an investment. A safe fixed return from a bank is calculated by the FD & RD Calculator, and a recurring deposit works much like a SIP with a fixed rate.
Common mistakes
- Treating the calculator's result as a promise.
- Using a high return rate to make the goal look reachable.
- Ignoring inflation when setting the target.
- Stopping the SIP when the market falls, which is when units are cheapest.
- Starting late and then trying to catch up with a very large amount.
- Choosing a fund because of last year's return alone.
Before you invest
A calculator does the arithmetic correctly, but it does not know your goals, your risk tolerance or your tax position. For decisions about which funds to buy, speak to a SEBI-registered investment adviser, and read the fund's official documents. This guide explains how the numbers work and is not investment advice.
Quick answers
Is the SIP result guaranteed? No. It is an estimate based on an assumed constant return.
How is the monthly rate calculated? The yearly return divided by 12, which is a common convention in fund calculators.
What is a step-up SIP? A SIP whose instalment rises by a fixed percentage each year.
How much should I invest? A common starting point is a fixed share of income that you will not need for years, but the right amount depends on your goals and expenses.
Is my data stored? No. The calculation happens in your browser.