Savings Calculator
Project your savings account balance from a starting amount, monthly deposits, and your APY — with the interest broken out so you can see your money working.
| Year | Deposits to date | Interest to date | Balance |
|---|
How the projection works
Each month, your balance earns one month of interest at your APY's equivalent monthly rate, then your deposit is added:
Balancenext = Balance × (1 + monthly rate) + Deposit
Start $1,000, deposit $300/mo at 4.5% APY for 5 years:
Deposits: $19,000 · Interest: ≈ $2,290 · Final balance: ≈ $21,290
You deposit $5,000 once and add nothing further, at 4.5% APY for 20 years. Since the monthly-equivalent rate compounds to exactly 4.5% every 12 months, the 20-year multiplier is 1.04520 = 2.4109.
Final balance = 5,000 × 2.4109 = $12,055 — your original $5,000 plus $7,055 of interest, entirely from compounding with zero additional contributions.
The cost of waiting to start
| Years saving $300/mo at 4.5% APY | Final balance |
|---|---|
| 10 | $45,162 |
| 20 | $115,218 |
| 30 | $224,070 |
| 40 | $393,441 |
The same $300/month deposit produces wildly different outcomes depending purely on how long it compounds — 40 years of saving is worth more than triple 20 years' worth, not double, because the earlier dollars have decades longer to compound. Waiting even 10 years to start (30 years instead of 40) costs about $169,000 in this example, more than the total of everything deposited during those 10 "waited" years.
Common savings-projection mistakes
- Comparing balances across different time horizons without noticing the horizon difference. As the table above shows, the gap between 30 and 40 years of saving dwarfs the gap between 20 and 30 — time matters more than most people expect.
- Assuming a lump sum with no further deposits won't grow meaningfully. A single $5,000 deposit still more than doubles over 20 years at a decent APY, as the second worked example shows — compounding works on lump sums too, not just regular contributions.
- Using the nominal rate instead of APY when comparing offers. Two accounts advertising slightly different "interest rates" can have the same APY once compounding frequency is accounted for — always compare APY to APY.
Making your savings work harder
Three practical upgrades, in order of impact. Rate: the national-average savings account pays under 0.5% APY while high-yield accounts pay several points more — on the example above, that difference alone is worth about $2,000 over 5 years. Automation: a transfer on payday makes the deposit happen before spending can claim it. Purpose: give the account a job — an emergency fund target or a specific savings goal — because named money is spent less. For funds you won't touch for years, compare a CD ladder or, on long horizons, investing.
Frequently asked questions
How much will my savings grow in 5 years?
$1,000 + $300/mo at 4.5% APY ≈ $21,300 after 5 years ($19,000 deposits, ~$2,300 interest).
What is APY and how is it different from the interest rate?
APY includes compounding — it's the true annual yield and the number to compare between banks.
Where should I keep my savings?
Near-term money: high-yield savings or money market (FDIC-insured, liquid); CDs for a bit more yield; invest longer-horizon money.
How much does a lump sum alone grow without deposits?
$5,000 at 4.5% APY for 20 years, no further deposits, grows to about $12,055 — $7,055 of pure compounding interest.
How much does starting late actually cost?
A lot — $300/mo at 4.5% APY for 40 years is ~$393,441, but for 30 years (10 years later) it's ~$224,070, a ~$169,000 gap from one decade of delay.
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Note: Assumes a constant APY; bank rates change with the market. Not financial advice. Last reviewed: September 2026.