Sinking Funds Explained: How They Work and How to Start

The short answer

A sinking fund is money you set aside a little at a time for a specific expense you know is coming, so it does not hit your budget all at once. To work out the monthly amount, divide the total cost by the number of months until it is due. For example, a 600 insurance bill due in 12 months needs 50 set aside each month.

What a sinking fund actually is

Most budgets handle the weekly and monthly basics well enough: rent, groceries, power, phone. They struggle with the costs that arrive once or twice a year. Car registration, annual insurance, a family holiday, Christmas, a vet bill, a laptop that is nearing the end of its life.

None of these are emergencies. You knew they were coming. But if you have not saved for them, they feel like emergencies, and they often end up on a credit card.

A sinking fund fixes that by spreading the cost across the months before it is due. The name comes from an old finance term for money put aside to pay off a debt over time, but in personal budgeting it simply means a named pot of savings with a purpose and a target date.

Sinking fund versus emergency fund

People mix these up, so it helps to separate them.

	Sinking fund	Emergency fund
Purpose	A known, planned expense	An unexpected event
Amount	Calculated from the cost	A buffer you choose, often a few months of essentials
Timing	You know roughly when	You do not know when, or if
Number of pots	Several, one per expense	Usually one
Example	Annual car insurance	Job loss, urgent repair

Both are useful. A sinking fund keeps predictable costs from draining your emergency fund. If your emergency fund keeps getting spent on things that were really predictable, that is a sign you need more sinking funds.

The formula

The arithmetic is simple:

Monthly amount = (target cost minus amount already saved) divided by months until due

A few worked examples:

• Car registration of 840, due in 8 months, nothing saved yet: 840 divided by 8 is 105 a month.
• A holiday costing 2,400 in 10 months, with 400 already saved: (2,400 minus 400) divided by 10 is 200 a month.
• Christmas spending of 900, due in 11 months, with nothing saved: 900 divided by 11 is about 82 a month.

If you are paid fortnightly or weekly, you can divide the monthly figure by the number of pay periods in a month instead, or divide the yearly cost by the number of paychecks in the year. Either approach works, as long as the total reaches the target by the due date.

Which expenses suit a sinking fund?

Look at your last 12 months of statements and pick out anything that was large, infrequent or predictable. Common candidates:

Home and vehicle

• Car registration, roadworthy or inspection costs
• Car servicing and tyres
• Home and contents insurance
• Home maintenance, such as a hot water system or appliance replacement
• Council tax, rates or strata levies if paid in lumps

Family and life

• Christmas and gifts
• Birthdays
• School fees, uniforms and supplies
• Annual memberships and subscriptions
• Holidays and travel

Health and pets

• Dental and optical
• Vet bills and pet insurance
• Prescription costs that arrive in a block

Money admin

• Annual professional fees, such as an accountant
• Tax bills if you are self-employed (check with an accountant before deciding the amount)
• Technology replacement, such as a phone or laptop

You do not need all of these. Start with the three or four that caused you the most trouble last year.

How to set sinking funds up, step by step

1. List the costs

Write down each expense, the amount, and the month it falls due. If you are not sure of the amount, use last year’s figure and add a small buffer for price rises.

2. Calculate the monthly amount

Use the formula above for each one. Then add them all up. That total is your monthly sinking fund commitment.

3. Check it fits

Compare the total with your budget. If it is more than you can afford, you have two choices: lower the target, such as a smaller Christmas budget, or lengthen the timeline. Do not skip the fund altogether. A smaller contribution is better than none.

4. Choose where the money sits

You have three common options:

• One savings account, tracked in a spreadsheet. Everything sits in a single account, and your sheet records how much belongs to each fund. This is the simplest to set up and works well with banks that charge for extra accounts.
• Separate accounts or sub-accounts. Some banks let you create named savings buckets. This gives a clear visual, but it can get fiddly with 10 or more funds.
• Cash envelopes. Physical envelopes for small, frequent funds, such as gifts. Less secure, but some people find them motivating.

Whatever you choose, keep the money somewhere you will not be tempted to spend it, ideally a savings account that earns some interest.

5. Automate the transfer

Set up a recurring transfer on payday for the total amount. Automation removes the monthly decision, which is where most plans fail.

6. Track and adjust

Each month, record what went into each fund. When a bill comes due, pay it from the pot and reset the fund for next year. If a cost changes, recalculate the monthly amount.

A simple example

Imagine a household with these funds:

Fund	Target	Months left	Monthly
Car registration	840	8	105
Home insurance	1,200	11	109
Christmas	900	11	82
Holiday	2,400	6	400
Vet and pet costs	600	12	50

(The monthly figures are rounded.) The total comes to about 746 a month. That might sound like a lot, but it replaces a string of large, stressful hits during the year with a steady, predictable amount. If the total is more than the household can manage, they might lengthen the holiday timeline, which drops the biggest figure.

Tracking sinking funds in a spreadsheet

A spreadsheet is ideal for sinking funds because the calculations repeat. For each fund you need:

• Fund name
• Target amount
• Target date
• Amount saved so far
• Months remaining (a date formula, such as =DATEDIF(TODAY(), D2, "m"))
• Monthly amount needed (=(B2-E2)/F2)

Add a progress column showing saved divided by target, and you can see at a glance which funds are on track.

If you would rather not build the formulas yourself, the Sinking Funds Tracker spreadsheet lets you add up to 15 funds with a goal and a target date, then shows what to set aside each month. The Chalkline Money System 2027 includes the same tracker alongside a budget, bill calendar and savings goals, so the sinking fund contributions flow into the rest of your plan.

Common mistakes

• Starting too many at once. Begin with three or four funds and add more as the habit settles.
• Forgetting to reset. After you pay the bill, restart the fund for next year.
• Raiding a fund for something unrelated. If you do need to borrow from one, write down that you owe it back and by when.
• Using last year’s price. Insurance and registration costs often change. Update the target each year.
• Treating the money as spare. A balance of 1,000 in a sinking account is not a windfall. It is already spoken for.

Frequently asked questions

How many sinking funds should I have?

Enough to cover the large, predictable costs you had last year, and no more. Most households start with three to six and may grow to ten or more over time. If tracking becomes a burden, combine similar items into one fund, such as “Car costs”.

Do sinking funds need separate bank accounts?

No. You can hold all the money in one savings account and track each fund in a spreadsheet. Separate accounts or sub-accounts are a preference, not a requirement.

What if I cannot afford all my sinking funds?

Reduce the targets or lengthen the timelines before dropping a fund altogether. A smaller regular contribution still reduces the size of the bill you face later. You can also fund the most important ones first, such as insurance and registration.

Should I pay off debt or build sinking funds first?

That depends on your situation, and it is worth talking to a qualified adviser or a free financial counselling service if you are under pressure. Many people do both in parallel by keeping sinking contributions modest, so predictable costs stop adding to the debt.

If you want a ready-made way to plan and track your funds, the Sinking Funds Tracker is built for exactly that.