Asset Allocation Calculator Formula

Understand the math behind the asset allocation calculator. Each variable explained with a worked example.

Use the Asset Allocation Calculator

Formulas Used

Recommended Stock %

stock_allocation = round(base_stock_pct)

Recommended Bond %

bond_allocation = round(100 - base_stock_pct)

Years to Retirement

years_remaining = years_to_retire

Expected Return (Approx)

expected_return = base_stock_pct / 100 * 10 + (100 - base_stock_pct) / 100 * 4

Variables

VariableDescriptionDefault
ageYour Age(years)35
risk_toleranceRisk Tolerance1
retirement_ageTarget Retirement Age(years)65
years_to_retireDerived value= max(retirement_age - age, 0)calculated
base_stock_pctDerived value= min(max((120 - age) * risk_tolerance, 10), 95)calculated

How It Works

Asset Allocation by Age

The Classic Rule

Stock Allocation = (120 - Age) x Risk Multiplier

Older versions used 110 or 100 instead of 120, but increasing life expectancies favor more aggressive allocations.

Risk Tolerance Adjustments

  • Conservative (0.8x): Less volatility, lower expected return
  • Moderate (1.0x): Balanced approach, standard rule
  • Aggressive (1.2x): More stocks, higher expected return and volatility

    • Why This Works

    Younger investors have more time to recover from downturns, so they can hold more stocks. As retirement approaches, shifting toward bonds reduces the risk of a devastating loss at the wrong time.

    Worked Example

    35-year-old, moderate risk tolerance, retiring at 65.

    age = 35risk_tolerance = 1retirement_age = 65
    1. 01Base stock % = (120 - 35) x 1.0 = 85%
    2. 02Bond allocation = 100% - 85% = 15%
    3. 03Years to retirement = 30
    4. 04Expected return = 85% x 10% + 15% x 4% = 9.1%

    Frequently Asked Questions

    Is the age-based rule accurate?

    It is a useful starting point but overly simplistic. Your actual allocation should also consider income stability, existing savings, pension or Social Security, risk capacity, and personal comfort with volatility.

    Should I include international stocks?

    Yes. Most financial advisors recommend 20-40% of your stock allocation in international equities for diversification. This calculator shows the overall stock/bond split; you subdivide from there.

    What about other asset classes?

    Real estate (REITs), commodities, and alternatives can be included as part of your stock allocation for diversification. Keep your core allocation simple, then add complexity as your portfolio grows.

    Ready to run the numbers?

    Open Asset Allocation Calculator