From monthly saving to a future balance
This model makes equal investments at month-end and compounds monthly. It does not include an initial lump sum; use the compound interest calculator when you already have money invested. The annual return is divided by twelve to obtain a monthly periodic rate.
The result is M × ((1 + r)^n − 1) ÷ r, where M is the monthly amount, r the monthly rate and n the number of months. At a zero rate, it becomes M × n. A systematic investment plan describes the contribution habit; it does not establish a particular return.
A worked example without a performance promise
Investing 500 a month for fifteen years means depositing 90,000. With an illustrative 8% nominal annual return compounded monthly, the model ends at approximately 173,019.11. Setting the return to zero gives 90,000. The difference between those scenarios is assumed investment growth, not additional saving.
Try a shorter horizon before choosing a larger return assumption to close a gap. A goal that needs unusually strong performance may require a different saving amount, deadline or spending target.
What regular investing does not solve
A regular contribution schedule can make the process easier to maintain, but it cannot remove concentration, valuation or loss risk. A narrow sector fund and a diversified portfolio can have very different outcomes despite identical monthly deposits.
This tool does not deduct fees, taxes or inflation. Use the compound interest calculator for those explicit inputs. It also excludes missed deposits, changing contributions and investment volatility. Money needed soon requires a different risk discussion from a distant goal.
Questions readers often ask
Are contributions made at the start of each month?
No. This model assumes month-end contributions. Earlier deposits would have more time to compound.
Does this include fees and inflation?
No. Use the linked compound interest calculator to enter those assumptions.
Can I compare a zero-return case?
Yes. Enter 0 for the annual return; the balance then equals total contributions.
Is this an ETF recommendation?
No. The calculator does not select or recommend any investment.
Keep the result in context
The calculator uses simplified assumptions. It does not retrieve market prices, personalized tax rates or lender terms. Verify important inputs and revisit the estimate when circumstances change.
Understand ETFs, index funds and mutual funds · Use the research checklist · Financial information disclaimer
Further reading: Investor.gov financial planning tools.