Sinking Fund Calculator

Understanding Sinking Funds

A sinking fund is a specialized savings strategy where you set aside money gradually over time to pay off a known future expense or debt. Unlike a general savings account or an emergency fund, a sinking fund is designated for a specific, predetermined purpose with a clear target amount and deadline. Common examples include saving for a vehicle purchase, property tax, annual insurance premiums, business equipment replacement, or debt repayment. For related financial tools, check our Compound Interest Calculator and Annuity Calculator.

The Sinking Fund Formula

The mathematics of a sinking fund accounts for compound interest. When you make periodic deposits, each deposit accumulates interest over the remaining duration of the fund. To calculate the required periodic payment, we use the sinking fund factor formula:

Where:

• $A$ is the equal periodic deposit amount.
• $F$ is the future target amount (savings goal).
• $i$ is the periodic interest rate (annual interest rate divided by the number of compounding periods per year).
• $N$ is the total number of periods (years multiplied by the compounding periods per year).

Example Calculation

Suppose you want to accumulate $10,000 in 5 years to replace a piece of equipment, and you can earn an annual interest rate of 6% compounded monthly.

• Future Value Target ($F$) = $10,000
• Annual Rate = 6% (or 0.06 as a decimal)
• Compounding Frequency = Monthly (12 times per year)
• Periodic Interest Rate ($i$) = $0.06 / 12 = 0.005$
• Total Periods ($N$) = $5 \times 12 = 60$ monthly periods

Applying the formula:

You would need to deposit $143.33 monthly to reach your $10,000 target in 5 years.

Sinking Fund vs. Emergency Fund

While both involve saving money, they serve very different purposes:

• Emergency Fund: Set aside for unexpected, unplanned expenses (e.g., job loss, medical emergencies, sudden car breakdown). The target is usually 3 to 6 months of living expenses.
• Sinking Fund: Designated for expected, planned expenses (e.g., buying a car next year, paying quarterly taxes, annual holiday trips). You know when you will spend this money and exactly how much you need.