Savings Goal Calculator
Enter a target amount, current savings, fixed monthly deposit and annual interest rate (APR) to see exactly how many months until you hit the goal, the balance at the moment you cross the line, how much you will have deposited and how much came from interest. Great for planning a down-payment, emergency fund, wedding, big trip, or retirement target.
Please enter a valid number
Time to reach goal
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Balance at goal
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Total deposited
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Interest earned
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Uses the standard future-value-of-an-annuity formula, assuming deposits at month-end and monthly compounding. Real returns vary with market volatility, tax and withdrawal limits.
Formula
Monthly rate i = APR / 12 Months to goal n = ln((G·i + C) / (P·i + C)) / ln(1 + i) Balance at goal = P·(1+i)^n + C·((1+i)^n − 1) / i P = current savings, C = monthly deposit, G = target amount When i = 0 the formula degenerates to n = (G − P) / C
- · Uses the standard "future value of an ordinary annuity" formula, assuming each monthly deposit lands at month-end and earns interest from the following period. End-of-month timing is the most conservative (and the convention used by US/UK personal-finance tools).
- · If your account compounds daily or quarterly the answer drifts slightly faster or slower; for typical savings APRs the gap is < 1 % and can be ignored.
- · If your monthly deposit is 0 AND either your current savings are 0 or the rate is 0, the balance can never grow. The tool will flag that and ask you to add a deposit or switch to an interest-bearing account.
- · Typical APRs to plug in: HK time deposit ≈ 3–4 %; HK basic savings 0.5–1 %; index-fund auto-invest historically 5–8 % but with volatility; US high-yield savings 4–5 %; MPF default conservative fund ≈ 1 %.
- · Results are pre-tax and pre-inflation. Hong Kong does not tax interest, but overseas accounts (US brokerage, SG time deposits) may withhold tax. Inflation also erodes purchasing power by roughly 2–3 % per year.
- · Reference: standard annuity-future-value formula FV = P·(1+i)^n + C·[(1+i)^n − 1] / i, solved analytically for n. Source: any introductory corporate-finance textbook.
Frequently asked
I want to save $500,000 for a down-payment in 3 years — how much should I put aside each month?
For a 36-month target starting from $0 at 4 % APR: nudge the monthly deposit up until "time to reach goal" lands on exactly 3 years (36 months). The break-point is about $13,070/month, with ~$29,500 of interest earned along the way. If you already have $100,000 in the account, the required monthly drops to ~$10,260. Bumping the rate to 6 % (typical index-fund average) cuts it to ~$12,560 but adds volatility risk. The numbers are nominal — 3 years of ~3 % inflation means today's $500k feels like ~$540k in three years, so adding a 10 % buffer is prudent.
Why does seeding the account with even a small amount shorten the timeline so dramatically?
Because P (current savings) compounds from month 0 while C (monthly deposit) only starts compounding the month after it arrives. Example with a $100,000 goal, $500/mo, 4 % APR: starting from $0 takes ~143 months (11.9 years); starting from $10,000 takes ~135 months (11.25 years) — a small upfront amount shaves 8 months and lifts interest earned from $28k to $36k. The reason is that the $10,000 compounds for the full 11 years, generating far more interest than the $500 × 8 = $4,000 of extra deposits you would have made. Practically: "lump sum + monthly" always beats "pure monthly", even when the lump is small.
Does chasing a higher yield (e.g. 7 % index funds) really shorten the timeline that much, and what is the trade-off?
Yes — the speed-up is substantial, but volatility is the price. Same $100,000 goal, $500/mo, starting from $10,000: 1 % APR (basic savings) → ~157 months; 4 % APR (time deposit) → ~135 months; 7 % APR (index fund average) → ~120 months. Going from 1 % to 7 % shaves more than 3 years off the timeline. The trade-off is real risk: index funds can drop 20–40 % in any given year, and if that drawdown lines up with your deadline (e.g. saving for a house), your portfolio may sit below the goal with no time to recover. Rule of thumb: money needed within 5 years → low-volatility (time deposit / short bonds); money for 10+ years → equity index funds are reasonable; 3–10 year horizons → some blend (e.g. 60/40 stocks/bonds).
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