The short answer
Starting with $5,000 and adding $500/month at 4.5% APY (compounded monthly), 10 years grows to $83,717.50 — $65,000 of that is your own deposits, and $18,717.50 is interest earned. Want to reach $100,000 instead? Either keep depositing $500/month for about 11.7 years, or raise the monthly deposit to $609.56 to hit $100,000 in exactly 10 years.
Key takeaways
- This calculator runs three ways: project a balance forward (Future Value), solve for the deposit needed to hit a goal by a date (Monthly Deposit), or solve for how long a goal takes at your current deposit rate (Time to Goal).
- On $5,000 + $500/month at 4.5% for 10 years, interest earned ($18,717.50) is more than a quarter of the final $83,717.50 balance — compounding does real work even at a modest savings-account rate.
- Reaching a fixed goal faster costs more per month: hitting $100,000 in 10 years instead of the 11.7 years it would otherwise take requires raising the deposit from $500 to $609.56/month.
- Compounding frequency (daily, monthly, quarterly, annually) makes a small but real difference — more frequent compounding modestly increases the effective yield at the same stated rate.
Three ways to run the numbers
Future Value: $5,000 + $500/mo @ 4.5% for 10 years → $83,717.50
Time to Goal: same inputs, $100,000 target → 140 months (11.7 years)
Monthly Deposit: same rate, $100,000 target in exactly 10 years → $609.56/month
Each mode answers a different real-world question. Use Future Value when you know what you can save and want to see where it leads. Use Time to Goal when you have a fixed deposit amount and want to know when you'll get to a target — useful for open-ended goals like "build a 6-month emergency fund." Use Monthly Deposit when you have a deadline (a house down payment by a certain date, for example) and need to know exactly how much to set aside each month to hit it on schedule.
The deposit-vs-time trade-off
Holding the goal ($100,000) and starting balance ($5,000) fixed, there is a direct trade-off between how fast you get there and how much you deposit each month:
| Approach | Monthly Deposit | Time to $100,000 |
|---|---|---|
| Keep depositing $500/month | $500.00 | 11.7 years |
| Target exactly 10 years | $609.56 | 10.0 years |
Shaving 1.7 years off the timeline here costs about $110/month more — a concrete way to weigh "save faster" against "save comfortably" for your own goal. Try both the Monthly Deposit and Time to Goal modes with your real numbers to see where that trade-off lands for you.
Related calculators
- Compound Interest Calculator — explore compounding frequency and rate assumptions in more depth.
- CD Calculator — model a fixed-term certificate of deposit instead of an open savings account.
- Budget Calculator — find how much you can realistically set aside each month.