How this calculator works
Your current savings grow at the monthly equivalent of the interest rate. The monthly deposit is the amount whose growth, added to that, lands exactly on your goal at the end of the period. In “how long” mode the calculator simply adds your deposit and interest month by month until the goal is reached.
i = (1 + rate)^(1/12) − 1, N = months
Monthly deposit = (Goal − Saved × (1 + i)^N) × i ÷ ((1 + i)^N − 1)
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| What do you want to find? | Monthly amount to save |
| Savings goal | $50,000 |
| Already saved | $5,000 |
| Interest rate on savings | 4 %/yr |
| Time to reach goal | 5 years |
| Result | Value |
|---|---|
| Save each month | $663.61 |
| Months | 60 |
| Total you deposit | $39,816 |
| Interest earned | $5,184 |
Step by step:
- Monthly rate = 0.3274%, months = 60
- Current savings grow to $5,000 × 1.2167 = $6,083
- Still needed = $43,917
- Monthly deposit = needed × i ÷ ((1 + i)^N − 1) = $663.61
Common mistakes to avoid
- Keeping a short-term goal in volatile investments — money you need within a few years usually belongs in savings or CDs.
Frequently asked questions
How much should I save each month for a $50,000 goal in 5 years?
With $5,000 already saved at 4% interest, about $664 a month.