Lump Sum Investment Calculator
Got a bonus, an inheritance, or savings sitting idle? See what a one-time investment grows into — how long it takes to double, and what it's worth after inflation. No further deposits needed.
▸ Show year-by-year breakdown
| Period | Growth | In today's $ | Value |
|---|
Estimates are for illustration and education only — not financial advice. Returns are assumed constant and are not guaranteed.
Investing a lump sum, explained
A lump sum investment is the purest form of compounding: one deposit, no further contributions, just time and rate doing the work. The math is FV = P × (1 + i)n — and because growth is exponential, the last years of a long horizon add far more dollars than the first ones.
The rule of 72 — and the real doubling time
A quick mental shortcut: divide 72 by your rate to estimate how many years money takes to double (72 ÷ 8% ≈ 9 years). The calculator shows the exact figure. Every doubling stacks: at 7%, $25,000 doubles roughly every 10 years — so a 30-year horizon means about three doublings, turning it into ~$200,000.
Lump sum vs. investing gradually
Historically, investing a lump sum immediately has beaten spreading it out (dollar-cost averaging) about two-thirds of the time, simply because markets rise more often than they fall — more time in the market wins on average. Spreading it out reduces the regret of bad timing, though, which is a legitimate reason to prefer it. If you'd rather model gradual investing, use our compound interest calculator with monthly contributions.
Don't skip the inflation field
Long horizons make nominal numbers flattering. Setting the inflation field (historically ~2–3% in the US) shows the result in today's purchasing power — usually the more honest number for planning. The year-by-year table shows both side by side.
Doubling time by rate of return
How long a lump sum takes to double, and what one dollar becomes over 30 years, with monthly compounding.
| Annual return | Doubles in | $1 after 10y | $1 after 20y | $1 after 30y |
|---|---|---|---|---|
| 2% | 34.7 years | $1.22 | $1.49 | $1.82 |
| 4% | 17.4 years | $1.49 | $2.22 | $3.31 |
| 7% | 9.9 years | $2.01 | $4.04 | $8.12 |
| 8% | 8.7 years | $2.22 | $4.93 | $10.94 |
| 10% | 7.0 years | $2.71 | $7.33 | $19.84 |
Figures are rounded and assume a constant rate with monthly compounding — illustrative only.
How a lump sum compounds
With no ongoing contributions, a lump sum's growth is pure compounding — the same money earning returns on its returns, year after year.