Allocation Formula and Methodology
The calculator uses a multi-factor approach to determine your equity/bond split.
The base formula is stockPct = 110 - age, then adjusted by risk tolerance (+/-12 points), capped by time horizon (under 3 years: max 25%, under 7: max 45%, under 12: max 60%), and nudged by target return (8%+: +4 points, 4%-: -6 points).
The final percentage is clamped to 15-90%.
cashReserve = min(emergencyFund, totalInvestment)
investable = max(0, totalInvestment - cashReserve)
stockPct = 110 - age // then adjust for risk, horizon, target
bondPct = 100 - stockPct
blendedReturn = (stockDollars x stockReturn + bondDollars x bondReturn + cashReserve x 2%) / totalInvestment
projectedValue = investable x (1 + r)^n + monthlyInvestable x 12 x ((1+r)^n - 1)/r + cashReserve
For a 40-year-old moderate investor with $100,000 (including $10,000 emergency fund) and $500/month over 15 years: stockPct = 70%, blendedReturn = 6.32%, projected value = $364,464.
Worked Example: Step-by-Step Calculation
A 40-year-old investor has $100,000 total, a $10,000 emergency carve-out, moderate risk tolerance, 15-year horizon, 6% target return, and $500/month contributions.
- Cash Reserve: min($10,000, $100,000) = $10,000. Investable: $100,000 - $10,000 = $90,000.
- Stock %: 110 - 40 = 70. Moderate: no adjustment. 15-year horizon: no cap. 6% target: no adjustment. Final = 70% stocks, 30% bonds.
- Dollar Allocation: $90,000 x 70% = $63,000 stocks. $90,000 x 30% = $27,000 bonds.
- Blended Return: ($63,000 x 8% + $27,000 x 4% + $10,000 x 2%) / $100,000 = 6.32%.
- Projected Value: $90,000 x 1.0632^15 + $450 x 12 x (1.0632^15 - 1)/0.0632 + $10,000 = $225,666 + $128,797 + $10,000 = $364,464.
- Total Growth: $364,464 - $190,000 contributions = $174,464.
Scenario Comparison Table
| Scenario | Age | Risk | Stock/Bond | Blended Return | Projected Value | Total Growth |
|---|---|---|---|---|---|---|
| Default moderate | 40 | Moderate | 70/30 | 6.32% | $364,464 | $174,464 |
| Conservative | 40 | Conservative | 58/42 | 4.92% | $310,661 | $120,661 |
| Aggressive | 40 | Aggressive | 82/18 | 7.94% | $439,064 | $249,064 |
| Young aggressive | 25 | Aggressive | 90/10 | 8.30% | $1,640,660 | $1,360,660 |
| Near-retirement | 55 | Conservative | 37/63 | 4.35% | $213,653 | $53,653 |
