§ Tools / Series 03 · Personal finance
Lump Sum Investment Calculator
The textbook future-value question: invest a one-time amount today at an expected annual return, and see what it is worth in N years. Compound interest, made honest — six compounding conventions, fees applied as a pre-compounding drag, tax on gains only, and the real (inflation-adjusted) value shown next to the nominal one.
§ Market-linked — not a fixed-rate product
This projects a one-time investment under an assumed return. Equity returns are not guaranteed and the smooth curve is not a forecast. To invest periodically instead, use the SIP calculator; to solve for the time to a goal, the investment time-to-goal calculator; to solve for the rate, the CAGR calculator.
6
Compounding modes
3
Scenarios
ln(2)
Exact doubling
Real
+ after-tax + after-fee
v1
Methodology
§ Start with a preset
Three starting points — adjust anything after.
Inputs
Pick an amount unit so a ₹1 crore lump sum doesn't need eight zeros · everything recomputes instantly.
Future value
$45,331.80
$10,000 invested today for 20 years at 8% (net 7.85% after fee), with annual compounding. That grows it 4.53×.
Total earnings$35,332
Doubling time9.2 yrs
After-tax value$40,032
Real value · today's money$27,665
Total deposited
$10,000
one-time, unchanged
Total earnings
$35,332
77.9% of corpus
Growth multiple
4.53×
353% absolute return
Doubling time
9.17
ln(2) / ln(1 + net) · exact
Fee drag · lifetime
−$1,278
0.15% annual expense
Effective annual yield
8.000%
annual compounding
§ Balance over time
Principal vs compound growth — and the inflection point
Y0Y3Y6Y9Y12Y15Y18Y20
Principal Compound growthReal value (today's money)
§ Compounding convention
The same 8% at every frequency
Annualselected
$45,332
8.000% eff.
Semi-annual
$46,645
8.160% eff.
Quarterly
$47,341
8.243% eff.
Monthly
$47,821
8.300% eff.
Daily
$48,058
8.328% eff.
Continuous
$48,066
8.329% eff.
§ Scenarios
Bear, base, bull — 3% either side of 8%
Bear5.0%
$25,785
Base8.0%
$45,332
Bull11.0%
$78,472
§ Sensitivity
Return × tenure — the future value across nearby assumptions
| Return ＼ Years | 12y | 16y | 20y | 24y | 28y |
|---|---|---|---|---|---|
| 5.0% | $17,653 | $21,335 | $25,785 | $31,163 | $37,663 |
| 6.5% | $20,934 | $26,779 | $34,257 | $43,823 | $56,060 |
| 8.0%base | $24,765 | $33,506 | $45,332 | $61,332 | $82,978 |
| 9.5% | $29,230 | $41,793 | $59,755 | $85,438 | $122,159 |
| 11.0% | $34,421 | $51,972 | $78,472 | $118,483 | $178,896 |
§ Year-by-year schedule
The path, not just the endpoint
| Year | Opening | Growth | Fee drag | Closing | Real closing |
|---|---|---|---|---|---|
| Y1 | $10,000.00 | +$785.00 | −$15.00 | $10,785.00 | $10,522 |
| Y2 | $10,785.00 | +$846.62 | −$17.38 | $11,631.62 | $11,071 |
| Y3 | $11,631.62 | +$913.08 | −$20.04 | $12,544.70 | $11,649 |
| Y4 | $12,544.70 | +$984.76 | −$23.01 | $13,529.46 | $12,257 |
| Y5 | $13,529.46 | +$1,062.06 | −$26.33 | $14,591.53 | $12,897 |
| Y6 | $14,591.53 | +$1,145.43 | −$30.03 | $15,736.96 | $13,570 |
| Y7 | $15,736.96 | +$1,235.35 | −$34.15 | $16,972.31 | $14,278 |
| Y8 | $16,972.31 | +$1,332.33 | −$38.73 | $18,304.64 | $15,023 |
| Y9 | $18,304.64 | +$1,436.91 | −$43.83 | $19,741.55 | $15,808 |
| Y10 | $19,741.55 | +$1,549.71 | −$49.49 | $21,291.27 | $16,633 |
| Y11 | $21,291.27 | +$1,671.36 | −$55.78 | $22,962.63 | $17,501 |
| Y12 | $22,962.63 | +$1,802.57 | −$62.74 | $24,765.20 | $18,414 |
| Y13 | $24,765.20 | +$1,944.07 | −$70.47 | $26,709.27 | $19,375 |
| Y14 | $26,709.27 | +$2,096.68 | −$79.02 | $28,805.94 | $20,387 |
| Y15 | $28,805.94 | +$2,261.27 | −$88.49 | $31,067.21 | $21,451 |
| Y16 | $31,067.21 | +$2,438.78 | −$98.96 | $33,505.99 | $22,570 |
| Y17 | $33,505.99 | +$2,630.22 | −$110.53 | $36,136.20 | $23,749 |
| Y18 | $36,136.20 | +$2,836.69 | −$123.32 | $38,972.90 | $24,988 |
| Y19 | $38,972.90 | +$3,059.37 | −$137.44 | $42,032.27 | $26,292 |
| Y20 | $42,032.27 | +$3,299.53 | −$153.03 | $45,331.80 | $27,665 |
§ Formula trace
- principal = 10000 × ones = 10000.00 USD
- netRate = 8% − fee 0.15% = 7.8500%
- futureValue = 10000.00 × (1 + 7.8500%/1)^(1×20) = 45331.80
- totalEarnings = FV − P = 35331.80 · growthMultiple = 4.5332×
- realFutureValue = FV / (1 + 2.5%)^20 = 27664.68
- afterTaxFV = P + max(gain,0) × (1 − 15%) = 40032.03
- feeDrag = FV(no fee) − FV = 1277.77 over 20y
- doublingYears = ln(2) / ln(1 + 7.8500%) = 9.17
§ Input audit
compoundingused
currencyused
expectedReturnPctused
feePctused
inflationPctused
initialAmountused
initialUnitused
returnVariancePctused
taxPctused
tenureYearsused
§ Warnings
- Projected returns are not guaranteed; a historical CAGR is not a forecast. Tax and fee handling are simplified.
§ Golden references · locked in tests
Three figures pinned so the compounding convention can't silently change.
1 @ 10% × 20y · annual
6.7275
₹1 lakh @ 15% × 60y · annual
₹43,83,99,874.57
Doubling @ 8% net · annual
9.01 yrs
The ₹1,00,000 → ₹43.84 crore figure over 60 years at 15% is the whole value proposition in one line: people systematically underestimate compounding over multi-decade horizons. Internal math runs at full precision; rounding is applied only at the display layer.
§ Specialized siblings
§ Same engine, headlessly
The deterministic projection, the compounding comparison, and the sensitivity matrix are reachable as stateless REST endpoints and MCP tools — this is the canonical example for the broader /api/v1/financial-calculators/* surface. Premium ticker prefill sits behind scoped API keys. Workbook CRUD is authenticated under calculator_id=lump_sum_investment.
GET/api/v1/financial-calculators · catalog
POST/api/v1/financial-calculators/lump-sum-investment/run
POST/api/v1/financial-calculators/lump-sum-investment/sensitivity
GET/api/v1/stocks/{ticker}/financial-calculators/lump-sum-investment/defaults · premium
MCP tools
calculate_lump_sum_investment · calculate_lump_sum_sensitivity · explain_lump_sum_formula · list_financial_calculatorsmethodology_version = financial-calculators.v1 · canonical = /en/tools/lump-sum-investment-calculator
§ FAQ
Four things worth knowing
Q01Why does the same 8% give different answers at different compounding frequencies?+
Because "8% compounded annually" and "8% compounded daily" are not the same yield. Annual turns 8% into exactly 8% a year; daily turns it into (1 + 0.08/365)^365 − 1 ≈ 8.328% effective. Over 30 years that gap is real money. This calculator exposes all six conventions — annual, semi-annual, quarterly, monthly, daily, and continuous (e^rt) — and the comparison table shows every one side by side so you can see what your bank or fund actually means.
Q02How are fees and taxes handled — and why does it matter?+
Fees are a pre-compounding rate drag: net rate = return − fee, so a 0.5% expense ratio over 30 years removes a multi-percent slice of the corpus, not a one-time 0.5% at maturity. Tax is applied to the positive gain only — never to your principal, and never on a loss. Most free calculators tax the whole future value, which is simply wrong. Both are first-class outputs with their own formula-trace lines.
Q03What is "real future value" and why is it lower?+
Real future value deflates the nominal corpus by inflation into today's purchasing power: FV / (1 + inflation)^years. A nominal number looks impressive after decades, but if prices roughly tripled over the same period, what it buys is far less. Surfacing the real value alongside the nominal one is the honest way to read a long-horizon projection.
Q04How long until my money doubles?+
doublingYears = ln(2) / ln(1 + net rate) — the exact, principled version of the Rule of 72, computed for your actual net (after-fee) effective yield rather than the rough divide-72-by-the-rate shortcut. At 8% it is about 9.0 years; the rule-of-72 guess of 9 happens to be close, but the exact figure drifts at higher and lower rates.