Endowment Spending Rate Calculator Formula

Understand the math behind the endowment spending rate calculator. Each variable explained with a worked example.

Use the Endowment Spending Rate Calculator

Formulas Used

Annual Spending

annual_spending = endowment_value * spending_rate_pct / 100

Sustainable? (spend <= real return)

sustainable = spending_rate_pct <= real_return ? 1 : 0

Real Return Rate

real_return_pct = real_return

Net Annual Endowment Growth

endowment_growth = endowment_value * (expected_return_pct - spending_rate_pct - inflation_rate_pct) / 100

Variables

VariableDescriptionDefault
endowment_valueEndowment Market Value($)50000000
spending_rate_pctAnnual Spending Rate(%)5
expected_return_pctExpected Annual Return(%)7
inflation_rate_pctInflation Rate(%)3
real_returnDerived value= expected_return_pct - inflation_rate_pctcalculated

How It Works

How Endowment Spending Works

Endowments are designed to provide perpetual funding. The spending rate must be low enough that investment returns preserve the real (inflation-adjusted) value of the endowment.

Formula

Annual Spending = Endowment Value x Spending Rate

Sustainable if Spending Rate <= Expected Return - Inflation

Common Practice

  • Most institutions spend 4-5% annually
  • The "Yale Model" suggests 5.25% with a diversified portfolio
  • Spending above the real return rate erodes the endowment over time

    • Worked Example

    A $50M endowment with 5% spending rate, 7% expected return, 3% inflation.

    endowment_value = 50000000spending_rate_pct = 5expected_return_pct = 7inflation_rate_pct = 3
    1. 01Annual spending: $50M x 0.05 = $2,500,000
    2. 02Real return: 7% - 3% = 4%
    3. 03Spending (5%) > Real return (4%): Not sustainable long-term
    4. 04Net growth: $50M x (7 - 5 - 3)/100 = -$500,000 per year

    Ready to run the numbers?

    Open Endowment Spending Rate Calculator