Sinking Funds: Meaning, Categories, and How to Calculate Each One

October 14, 2026 · Personal money

A sinking fund is money you put aside every month for a bill you know is coming but don’t pay monthly - car insurance, property tax, holiday gifts. To size one, divide what the bill will cost by the number of monthly deposits you have left before it’s due. With a full year to go and nothing saved yet, that’s the annual cost divided by 12. In the worked example below, 6 irregular bills totaling $7,140 a year become $595 a month.

Sinking funds meaning

The name comes from old finance: a company would “sink” money into a separate account, bit by bit, to repay a bond in one go when it came due. A household sinking fund works the same way. The expense is known in advance - you know roughly what it costs and when it falls - so it can be spread out instead of landing all at once.

That’s what separates it from an emergency fund. An emergency fund covers things you can’t schedule: a job loss, a medical bill, a broken furnace. A sinking fund covers things you can. A big bill you saw coming all year that still wrecks a month is a cash-flow problem, not an emergency. A sinking fund solves it.

How to calculate sinking funds

The formula for one fund:

Monthly deposit = (next payment - already saved) / deposits left before it’s due

Count deposits including the current month, assuming you deposit early in the month and the bill leaves later in it. When you are a full cycle ahead, this collapses to the familiar version:

Monthly deposit = annual cost / 12

That holds for bills paid in installments too. In the example, property tax of $3,600 a year is paid as 2 payments of $1,800. There are 6 deposits before each payment, so $300 a month covers it - the same $300 you get from $3,600 / 12.

Sinking funds categories: a worked example

These amounts are illustrative, not typical costs. Use your own bills:

Other categories worth a row, if they apply to you: car maintenance and tires, annual memberships, back-to-school costs, pet care, medical deductibles, home repairs, travel, and birthdays. The test for a category is simple: if it doesn’t come every month, but you can name it before it arrives, it belongs here. If you are paid every two weeks, the 50/30/20 budget calculator post shows how the extra paychecks can cover bills like these.

Starting late: the catch-up amount

The annual / 12 figure assumes each fund has a full cycle to fill. If you start in January, it doesn’t - every bill is closer than twelve deposits away. Each fund has to be paced to its own next payment:

The first month costs $1,082.50, which is $487.50 more than the steady $595. The annual subscriptions bill is due the same month you start, so its whole $120 goes in at once instead of $10 a month. That extra is temporary. Each fund drops back to its annual / 12 rate the month after its next payment goes out, and by September every fund in the example is on its steady rate and the total is back to $595.

The catch: one pot at the flat total

It’s tempting to skip the catch-up, open one savings account, and put the $595 total in every month from day one. Over a year it adds up to exactly the right amount. But the bills don’t arrive evenly, and from a standing start the pot runs dry before the deposits catch up. Here is the lowest balance the single pot reaches in its first year, depending on the month you start:

Starting from zero in 11 of the 12 months, the pot goes negative - by $1,685 if you start in April. Every one of those low points lands in October, the month of the second property tax payment. Only a November start, the month after that payment, gets through without a shortfall.

And it doesn’t fix itself. A year of flat deposits nets to exactly zero, so the same dip comes back every year. A January start is short by $590, and it will be short by that much each year until the gap is filled once.

So there are two honest ways to run it:

• Separate funds, each paced to its own due date (the catch-up table above). It costs more for the first months, then settles at the steady total, and no fund is ever short.
• One pot with a one-time cushion equal to the lowest balance for your start month - $590 for a January start in this example. After that, the flat $595 works year after year.

This is the part a simple “annual divided by 12” sheet leaves out: the division is right, but it describes where you end up, not how you start.

A sinking funds tracker: what it needs

A tracker needs one row per fund and these columns: what the fund is for, the next payment, the month it’s due, what is saved so far, deposits left, and this month’s deposit. The last one is the formula above, recalculated as you go.

Saved money lowers the deposit. In the January example, home insurance is $1,500 due in June, with 6 deposits left: $250 a month from nothing. If $300 is already in the fund, only $1,200 is left to save, and the deposit falls to $200. After the June payment it drops to $125 a month - the annual / 12 figure.

Sinking funds and the emergency fund

Sinking funds keep scheduled bills from turning into emergencies. That leaves the emergency fund for the unscheduled ones, and the same budget arithmetic sizes that fund too. On $4,000 of monthly net income with 70% of it committed to fixed costs, three months of income is $12,000, but three months of committed costs - the money that has to keep going out while something is wrong - is $8,400. These figures are illustrative too.

How these were calculated

Each bill’s monthly set-aside is its annual cost divided by 12, computed in whole cents and checked against the totals in the bill spreader below. The catch-up table counts deposits from the start month through each bill’s next due month, inclusive, with installment bills split evenly across their due months. The single-pot table is simulated month by month - a deposit at the start of the month, the bills paid during it - and computed a second way from running totals; the page only builds if the two agree. The emergency-fund figures come from the same code as the Committed Costs kit and are recomputed independently. All examples are illustrative. This is arithmetic, not financial advice.

If you want the annual-bills sheet on paper, this one sorts bills by the day they’re due and spreads the irregular ones into a single monthly set-aside, with the worked example above and blank rows for yours:

And if you’d rather have the sinking-funds calculation live in a spreadsheet, this workbook has one, alongside six other budget calculators for your own pay: