How savings actually grow
A savings balance grows from two sources: the money you put in and the interest it earns. Early on, your deposits do nearly all the work. Later — if you stay consistent — interest compounds on a bigger and bigger balance and starts contributing meaningfully on its own. This calculator models that process month by month: each month your balance earns interest at the APY you enter, then your deposit lands.
The savings formula
Where P is the starting deposit, D is the monthly deposit, r is the monthly rate (APY ÷ 12) and n is the number of months. The first term is your starting money grown; the second is the future value of all your monthly deposits, each compounding for the months it was in the account.
Deposits beat rates (for most savers)
Doubling your rate from 2% to 4% matters, but doubling your monthly deposit matters more — and you control the deposit. On a 10-year horizon starting from $5,000: saving $200/month at 4% ends near $36,904; saving $300/month ends near $51,629. Rate-shopping is worth an afternoon; a sustainable deposit habit is worth years.
Choosing the right home for savings
- Emergency fund (3–6 months of expenses): a high-yield savings account — safe, insured, instantly available.
- Known goal within 1–3 years (car, deposit, wedding): savings account or short CD ladder; avoid market risk on money with a deadline.
- Goals 5+ years away: investing usually out-earns interest, with risk — compare using the Investment Calculator.
Worked example
You start with $5,000, deposit $200 a month, and earn 4% APY for 10 years. You put in $29,000 of your own money and end with about $36,904 — roughly $7,904 of it interest. Leave the same plan running 20 years instead and interest contributes roughly $31,468 of the ~$84,468 total: time is the ingredient that turns small deposits into real money.
How to use this calculator
- Enter what you can start with today (zero is fine).
- Enter a monthly deposit you can sustain in a bad month, not just a good one.
- Enter the account's APY — high-yield savings accounts publish this clearly.
- Set the number of years and read the final balance and interest share.
- Try adding $50 a month or five more years to see what consistency is worth.
The head-start effect
Starting today with $5,000 and saving $200 a month beats starting in five years with the same deposit — by a wide margin — because the early money compounds longest. If you're waiting for the "right time" to start, run both scenarios above: the calculator will show you the cost of waiting in plain dollars.