What is a Sinking Fund?

Startups live and die by cash flow. You focus heavily on burn rate and runway. But there is a specific accounting tool that often gets ignored until it is too late.

It is called a sinking fund.

In simple terms, a sinking fund is money you set aside over time to pay off a specific debt or replace an asset. You are not saving for a vague rainy day. You are saving for a specific event that you know is coming.

Large corporations use these to pay off bond issues. For a founder, the concept is the same but the scale is different. It is about discipline. It prevents you from scrambling for capital when a large bill finally comes due.

It is easy to confuse these two concepts. They both involve holding cash in reserve. However, the intent is different.

An emergency fund is reactive. You build it because you do not know what will go wrong. You just know something eventually will. The amount is usually based on months of operating expenses.

A sinking fund is proactive. You know exactly what it is for. You know roughly when you need it. You can calculate the exact amount needed per month to reach the goal.

Here is how to think about the difference:

• Emergency Fund: The server room floods or a key client cancels a contract.
• Sinking Fund: You know your laptops will need replacing in three years or a tax bill is due in six months.

  

Founders often rely on the idea that future revenue will cover future costs. This is optimistic. It is also risky. If you have a large debt payment due in two years, assuming your Series B round will cover it is a gamble.

Using a sinking fund protects your working capital. When the expense arrives, the cash is already there. It does not eat into your payroll or marketing budget for that month.

Consider these common startup scenarios where this applies:

• Asset Replacement: Computers, machinery, and office furniture wear out. These are wasting assets. If you do not plan for their replacement, their failure becomes an emergency.
• Debt Repayment: If you have taken on venture debt or loans with balloon payments, setting aside small amounts monthly reduces the shock of the final payout.
• Taxes: Startups often get surprised by end of year tax liabilities. A sinking fund smooths this out.

The mechanics are straightforward. You do not need complex financial software to start.

First, identify the liability. Determine the total cost and the due date. Calculate the number of months between now and then. Divide the total cost by the months.

That creates your monthly contribution.

Keep this money separate. It should not be commingled with your general operating account. If it is mixed in, you will spend it. Place it in a high yield savings account or a low risk money market fund. The goal is preservation, not high returns.

Ask yourself a few questions as you review your balance sheet. What equipment is vital to our operation? When will it die? Do we have the cash to replace it today? If the answer is no, you likely need to start a sinking fund.