By Ashish Malaviya · First published 2/11/2026

How Much Should You Invest Monthly to Reach a Goal? A Reverse SIP Guide

A guide to reverse SIP calculations, future-value assumptions, time horizons and return sensitivity, using illustrative rupee examples rather than forecasts.

A reverse SIP calculation takes a target goal and calculates what you would need to contribute regularly to achieve this. Essentially you’re calculating how much you’d need to contribute each month to achieve your chosen target amount, based on your assumptions. This is a very useful tool to help you plan how you will achieve your goal but is not a prediction. The accuracy of the calculation will depend on how well you know how long you’ll be contributing for, when you’ll be contributing and what rate of return you’re assuming.

This can be useful to make a big goal feel more tangible. By putting a number and date on your goal (e.g. future education costs, a future purchase you want to make or long term savings) you can understand what you’re aiming for. However, you may need to factor in inflation for your goal amount and increase your contribution depending on changes in your income. Using a calculator can also help you have a discussion around your assumptions.

Know your goal

Start by writing down what the money is for and when you’ll need it. A goal such as ‘build wealth’ is too vague. You need to be specific with your goal. You could write ‘save an illustrative ₹8 lakh in 8 years’. This gives you something to work with but your target amount may not be exactly what you’ll need to pay in the future. If you’re saving for a future expense you may want to factor in that the price could go up.

How much do you currently have?

If you currently have some savings then your total to build will be less than if you have nothing. However, don’t include emergency savings or money for another commitment. Your goal should reflect how much really can be allocated towards it.

Maths behind the calculation

Most reverse SIP calculators use a future value calculation. This assumes you’re making regular monthly contributions, growing at a steady rate (converted to a monthly rate). This gives you an approximation of how much you’ll have. Most calculators will assume you’re contributing at the end of each month. This will slightly alter your answer.

Investment returns will not be a straight line. Investments linked to the market will fluctuate and your returns may be affected by charges and tax. Using a steady rate calculation helps you to see your assumptions and compare them. However, it won’t reflect every market scenario. Check how the calculator handles compounding, contribution dates, initial capital and charges.

Example in rupees

Let’s say your goal is to have an illustrative ₹8,00,000 in 8 years. This calculator may ask you to try several rates of return. The higher the rate you assume the less you’ll need to contribute each month. These are just hypothetical numbers. The lower the rate you assume the higher you’ll need to contribute each month. This is purely maths and doesn’t mean you can pick a higher rate of return to make the monthly figure look good.

It’s best to run at least three scenarios. One with a conservative rate of return, one with a moderate rate (just to compare) and one with a higher rate of return to see how sensitive your goal is. All results should be noted as illustrative. If you’re only achieving your goal with the highest rate of return then your goal may be quite uncertain. Just because you’re contributing an amount that looks affordable doesn’t mean you’ll achieve your goal.

Time

The longer you contribute for the more time your monthly contributions will have to build up and earn returns. This will often mean you’ll be able to achieve your goal with a lower monthly contribution. If you’re contributing for a shorter period of time you’ll generally need to contribute more as there will be fewer contributions and less compounding.

Check when your goal is. An 8 year goal is not the same as an 8 year and 6 month goal. If you’re contributing monthly the number of contributions and dates will affect how much you’ll need. Also check if your first contribution will be immediately or in one month. Don’t compare two calculators unless they have the same assumptions.

Sensitivity

Having one rate of return can give you a false sense of security. Increasing the rate by a little may mean your contribution decreases a lot and looks good. However, you don’t get to choose what happens in the market. Equity values could decrease, debt investments could have credit or interest rate risk and different funds will behave differently. Inflation will also affect how much you’ll have.

A useful way of seeing how sensitive your goal is is to change one assumption at a time. Start by keeping your goal and time frame the same but trying different rates of return. Next keep your rate the same but shorten the time frame. Finally think about increasing your goal as the cost may increase. This isn’t to give you a perfect prediction but to show you what your goal depends on the most.

Not a fixed contribution

Most basic reverse SIP calculations assume you’ll be contributing the same amount each month. In reality your salary could increase, decrease or be interrupted. Some households may be able to increase their contributions each year whereas others may need to decrease during times of unemployment or family expenditure. If you’re planning to increase your contributions in steps you’ll need to do a different calculation. The increases should be realistic.

If you’re reviewing your plan yearly you should check how much you’re contributing. If you’re missing out on contributions this can impact how much you have at the end, especially if it’s early on and you’ve lost out on compounding. Adding extra later may help but it will depend on how much you’re adding, when and what your actual returns are. Don’t use a calculator as a replacement for checking your plan against your cash flow.

Inflation

A goal of ₹8 lakh in the future may seem like a lot now but after several years of inflation it may not be as much. If your goal is related to education, healthcare or housing make sure you’re estimating how much it will cost in the future. When making assumptions around inflation make sure to label them as assumptions and review them using credible data when updating this article.

Inflation is not the same as investment returns. A nominal return is how much your investment has increased in rupees. A real return takes into consideration how much your purchasing power has changed after inflation. Whilst your calculator may be mathematically accurate you may not have enough to buy the products/services you wanted. Your goal should reflect what it will be used for in the real world.

Understanding your answer

Your answer will give you a rough idea of how much you’ll need to contribute each month. Think about whether this fits with your essential expenditure, debt repayments and cash buffer. If not you should consider changing your goal, time frame or contributions. Don’t assume you’ll get a better return by being an aggressive investor. Some goals can be delayed or come from multiple sources whereas others will be on a fixed date. You’ll need to make practical decisions based on your goal and household.

The investment

A calculator won’t tell you what mutual fund or investment to use. Your risk, liquidity, charges, tax and when you need the money will all impact whether it’s suitable for your goal. Just because you’re contributing for a longer period of time doesn’t mean all high risk investments will be suitable. You may need to go for something with less volatility but it may not keep up with inflation.

Common mistakes

Don’t mix up annual percentage returns and monthly rates. Make sure to check how the calculator converts these. Don’t forget to include any initial lump sum. Don’t assume you’ll definitely have the amount shown. Don’t forget to include costs.

Don’t be tempted to use a calculator that gives a very specific figure in rupees. Make sure you understand what the inputs are.

Setting a goal based on an unrealistic contribution amount. It may be more honest to start with a lower recurring contribution that fits within your household budget. If you have a large contribution amount but pause it after a few months this may not be the best approach. If your income, family commitments, cost of goal or date changes make sure to review your plan.

Conclusion

Reverse SIP planning will help you see how much you may need to contribute to achieve your future goal based on your assumptions. It’s useful to understand how your goal amount, time frame, contribution and sensitivity to returns will impact your goal. It’s not a guarantee and your real investment journey won’t be as straightforward as a formula. Try several scenarios, factor in inflation and costs and make sure you understand the assumptions made by the calculator.

Goal worksheet

Start by writing down your goal amount, when you’ll need the money, how much you’ve already set aside and how much you can contribute each month without borrowing. Note down the assumptions you made around your returns and when the calculator assumes you’ll be making deposits. Write down your inflation assumptions separately and if you plan to increase your contributions each year. This will help you see why you may be getting a disappointing result based on your goal, time frame or contribution.

If your goal changes make sure to review your worksheet. If your course fee has increased you may need to update your goal. If your salary has increased you may be able to increase your contributions. If your income is uncertain you may need to reduce your contribution schedule. All changes should be made honestly.

Buffer

If your goal is calculated to the last rupee you’ll have no buffer for returns not being as high as assumed, missing out on contributions or the cost increasing unexpectedly. This can be done by increasing your goal amount or reducing your return assumption. How much of a buffer you should have will depend on your goal and household. There is no one percentage that will guarantee your investment.

The most useful thing a calculator can do is show you how fragile your goal is. If your goal looks unachievable with a small change in your assumptions this is useful to know early on.

Continue reading

• Learn the basics in What Is a SIP?.
• Calculate an illustrative monthly amount with the SIP calculator.

Educational information only. Verify current rules and consider qualified advice for personal decisions.