Living Off Retirement Interest Calculator

How the Calculator Works

The calculator uses a simple compound interest model to estimate how long your retirement savings can last if you only withdraw the interest earned each month. Here's how it works:

1. You start with an initial investment amount.
2. Each month, you earn interest on your current balance.
3. You withdraw a fixed amount each month from the interest earned.
4. The calculator tracks how long your balance remains positive.

This approach assumes you never touch your principal investment, which can be a conservative strategy for retirement planning.

The Formula

The calculation is based on the following formula for the number of months your savings can last:

Where:

• Initial Investment - The amount of money you start with
• Interest Rate - The annual interest rate (as a decimal)
• Monthly Withdrawal - The fixed amount you withdraw each month

This is a simplified model that assumes the interest rate remains constant and you never withdraw from the principal.

Worked Example

Let's say you have $100,000 invested at a 4% annual interest rate, and you want to withdraw $1,000 per month from the interest earned.

1. Convert the annual interest rate to monthly: 4% ÷ 12 = 0.333% or 0.00333 as a decimal
2. Calculate the monthly interest earned: $100,000 × 0.00333 = $333.33
3. Determine how many months you can withdraw $1,000: $333.33 ÷ $1,000 = 0.333 months

This means your $100,000 investment would only last about 1 month if you withdrew $1,000 per month from the interest earned. This example shows how important it is to carefully plan your retirement withdrawals.

Key Considerations

When using this calculator, keep these points in mind:

• The calculation assumes you never touch your principal investment
• Real-world interest rates may change over time
• Inflation can reduce the purchasing power of your withdrawals
• This is an estimate - actual results may vary