Two sources of a future balance
A compound-growth projection combines money you put in with a hypothetical return on the growing balance. These are different things. Always inspect contributions and growth separately before treating a large future total as investment performance.
For example, an initial 1,000 plus 100 at the end of every month contributes 2,200 during the first year. With an assumed 0% return, the year-end balance must also be 2,200. This is a useful check on both the formula and your interpretation of the result.
How our monthly model works
Each month, the existing balance receives one-twelfth of the assumed nominal annual return. The monthly contribution is then added. Because the contribution arrives at the end of the month, it first earns a return in the next period. A beginning-of-month contribution would produce a different answer.
Try the compound calculator with the same contributions and three assumed rates. A low, middle and high scenario illustrates sensitivity; none is a promise. The model does not simulate changing market returns or the sequence in which gains and losses occur.
Costs that are outside the result
Taxes, platform charges, fund expenses and inflation can reduce what the balance buys. If you use a return after fees, document that assumption. Do not subtract the same fee a second time. The inflation calculator can help explore purchasing power using a separate assumed rate.
For a fixed cash target with no assumed return, use the savings goal tool. That simpler calculation is often easier to budget against than a growth projection.