How Much to Invest Monthly Calculator
Use this calculator to estimate how much you need to invest each month to reach a future balance. It is one of the most practical long-tail scenarios because people rarely ask for a formula first. They ask what monthly amount is required.
How to use this page
This result assumes monthly compounding and monthly deposits made at the end of each month. It is designed for planning. Once you know the approximate contribution you need, move to the main compound interest calculator to compare different frequencies and timing assumptions.
What changes the result most?
- Longer time horizons lower the monthly amount needed.
- Higher expected returns help, but time and consistency usually matter more.
- A larger starting balance reduces the saving burden immediately.
Related pages
Working backwards from a target
Forward projections answer “what will I have?”. This one answers the question people actually have: “what do I need to put in?”. Using this page's defaults — $100,000 target, $10,000 already invested, 15 years, 7% compounded monthly — the answer is about $225.61 a month.
| Timeline | Monthly needed | Total you contribute | Supplied by growth |
|---|---|---|---|
| 5 years | $1,199 | $71,926 | 18% |
| 10 years | $462 | $55,397 | 35% |
| 15 years | $226 | $40,610 | 49% |
| 20 years | $114 | $27,465 | 63% |
| 25 years | $53 | $15,830 | 74% |
The relationship is steeply non-linear. Halving the timeline does far more than double the monthly requirement, because you lose both the contributions you would have made and all the compounding those contributions would have earned. This is the same fact that makes starting early valuable, stated from the other end.
What to do when the number comes back too high
- Extend the timeline first. It is the cheapest adjustment available and usually the least painful. Adding five years to the plan above drops the monthly requirement from $226 to $114.
- Then reconsider the target. Round numbers make poor goals. A target derived from what the money is for is easier to hit and easier to justify.
- Then cut costs, not corners. Reducing fees raises the effective rate without raising risk.
- Do not raise the rate to make it fit. Changing the assumption changes the spreadsheet, not the outcome. It is the most common way a plan fails silently.
If the requirement is comfortably affordable, the useful move is the opposite: keep the contribution and shorten the timeline, or keep both and treat the surplus as protection against a poor decade.
Questions about working backwards from a goal
How much should I invest each month?
It depends entirely on the target and the timeline. For $100,000 in 15 years starting from $10,000 at 7%, about $225.61 a month. Change any one of those and the answer moves substantially.
What return should I assume when working backwards?
A conservative one. At 5% rather than 7% the same goal needs about $295 a month instead of $226. Planning at the lower figure and treating better returns as margin is the safer error to make.
Should I include employer contributions?
Yes, if they are going into the same pot. Employer matching is an immediate return on your contribution before any market growth, and excluding it will overstate what you personally need to add.
What if my income is irregular?
Work out the annual total you can commit and divide by twelve for planning, then contribute when you can. The arithmetic here assumes even deposits; uneven ones with the same annual total land close enough.
Already know your monthly deposit?
This tool solves for the deposit needed to reach a target. To find the future balance from a deposit you already know, use the investment growth calculator. For a cash savings target, see the savings goal calculator.