Three ways to ask the question
Deposit needed: you know the goal and the deadline and want the monthly amount. Time needed: you know what you can put aside each month and want to know when you get there. End balance: you want to see what a regular deposit grows to. The tabs switch between them; the inputs that stay the same — what you already have and the account's APY — carry across.
The table shows the first mode for common goals starting from zero in an account paying 4% APY. Interest helps, but for short horizons the deposit does almost all the work: over one year, interest covers about 2% of a goal; over five years, about 10%.
| Goal | In 1 year | In 2 years | In 3 years | In 5 years |
|---|---|---|---|---|
| $5,000 | $409.22 | $200.60 | $131.09 | $75.55 |
| $10,000 | $818.43 | $401.19 | $262.18 | $151.11 |
| $25,000 | $2,046.09 | $1,002.98 | $655.46 | $377.76 |
| $50,000 | $4,092.17 | $2,005.97 | $1,310.92 | $755.53 |
| $100,000 | $8,184.35 | $4,011.94 | $2,621.84 | $1,511.05 |
How much the interest rate matters for short-term savings
Less than people expect. Saving $300 a month for three years on top of $2,000 ends within a few hundred dollars of the same place whether the account pays 0.5% or 5%. Rate shopping is still worth a few minutes — a high-yield savings account paying 4% versus a big-bank account paying 0.5% is several hundred dollars over three years for no extra risk — but the deposit, not the rate, gets you to a short-term goal.
| APY | End balance | Interest earned |
|---|---|---|
| 0.5% | $12,909.09 | $109.09 |
| 1% | $13,018.87 | $218.87 |
| 2% | $13,240.49 | $440.49 |
| 3% | $13,464.88 | $664.88 |
| 4% | $13,692.05 | $892.05 |
| 5% | $13,922.04 | $1,122.04 |
How long a goal takes at different deposits
With a $25,000 goal, $2,000 saved and 4% APY, the Time tab gives the months to the goal for any deposit. Doubling the deposit roughly halves the time; the interest column shows how much the account contributes at each pace — more when the money sits longer.
| Monthly deposit | Time to goal | You deposit | Interest |
|---|---|---|---|
| $100.00 | 13 yr 8 mo | $16,355 | $6,645 |
| $200.00 | 7 yr 11 mo | $19,020 | $3,980 |
| $300.00 | 5 yr 7 mo | $20,160 | $2,840 |
| $500.00 | 3 yr 6 mo | $21,201 | $1,799 |
| $750.00 | 2 yr 5 mo | $21,772 | $1,228 |
| $1,000.00 | 1 yr 10 mo | $22,072 | $928 |
Sizing an emergency fund
The commonest savings goal is a cushion of three to six months of essential expenses — rent or mortgage, utilities, food, insurance, minimum debt payments — not of income. For a household spending $4,000 a month on essentials, three months is $12,000 and six is $24,000. Build it in a high-yield savings account where it is reachable in a day; it is insurance, not an investment, so the return is secondary to it being there. Start with one month, which covers most surprises, and keep going.
| Cushion | Goal | Deposit to build in 1 year | In 2 years |
|---|---|---|---|
| 3 months | $12,000 | $982.12 | $481.43 |
| 6 months | $24,000 | $1,964.24 | $962.86 |
| 9 months | $36,000 | $2,946.37 | $1,444.30 |
| 12 months | $48,000 | $3,928.49 | $1,925.73 |
APY, compounding and how the math works
Banks advertise APY — annual percentage yield — which already includes compounding: $1,000 at 4% APY is $1,040 after a year regardless of whether interest is credited daily or monthly. The calculator converts APY to an equivalent monthly rate, (1 + APY)^(1/12) − 1, and applies it to each month's balance after adding the deposit. The formulas are the standard time-value-of-money ones: end balance = P(1 + i)^n + D × [(1 + i)^n − 1] ÷ i, solved for D or n as needed.
- Deposits are made at the end of each month; deposit at the start and you earn one extra month on each.
- APY is treated as guaranteed for the whole period; savings rates float, so revisit the plan when your bank changes its rate.
- Interest on savings is taxable as ordinary income outside tax-advantaged accounts; the figures here are pre-tax.
Where to keep goal savings
For goals under about three years, the choice is between a high-yield savings account, a money-market fund and a CD ladder; all are safe and the differences are small. For goals further out, the investment calculator covers the trade-off between a higher expected return and the risk of a shortfall at the wrong moment. A common rule: money you will need within five years stays in cash-like accounts.