What is a sinking fund?

A sinking fund is money you set aside gradually for a known future expense. Unlike an emergency fund (which is for unknown expenses), a sinking fund is for expenses you can predict — car registration, insurance, Christmas, holidays, annual subscriptions, car maintenance.

The name comes from the idea that you "sink" a little money into the fund each pay, so the total is there when the expense arrives. It's one of the most effective budgeting techniques because it eliminates the stress of irregular costs.

Sinking funds vs emergency funds vs savings goals

These three are often confused, but they serve different purposes:

• Emergency fund: for unknown, unexpected expenses — a car breakdown, a medical bill, a job loss. You don't know when or what. See our guide to savings goals.
• Sinking fund: for known, predictable expenses — car rego, insurance, Christmas. You know when and roughly how much.
• Savings goal: for a specific target — a house deposit, a holiday, a new car. You set the target and the timeline.

The difference matters because the approach is different. An emergency fund needs to be accessible and stable. A sinking fund needs to build to a specific amount by a specific date. A savings goal has a target and a timeline.

Step 1: Identify your sinking funds

List the irregular expenses you know are coming. Go through your bank statements for the last 12 months and note every expense that wasn't a regular monthly bill:

| Expense | Amount | When | Frequency | |---|---|---|---| | Car registration | $600 | March | Annually | | Car insurance | $800 | April | Annually | | Home insurance | $1,200 | April | Annually | | Council rates | $900 | Dec, Mar, Jun, Sep | Quarterly | | Christmas | $800 | December | Annually | | Car service | $400 | Every 6 months | Semi-annually | | Birthday gifts | $300 | Spread through year | Annually | | Holiday | $1,500 | July | Annually | | Total | $6,500 | | |

Step 2: Calculate the per-pay contribution

For each sinking fund, calculate how much you need to save per pay to have the amount ready by the due date.

Example: car registration due in 6 months

• Amount: $600
• Months until due: 6
• Monthly contribution: $600 ÷ 6 = $100/month
• Fortnightly contribution: $100 ÷ 2 = $50/fortnight

Example: Christmas in December (3 months away)

• Amount: $800
• Months until due: 3
• Monthly contribution: $800 ÷ 3 = $267/month
• Fortnightly contribution: $267 ÷ 2 = $134/fortnight

The total per-pay contribution

Add up all the per-pay contributions:

| Fund | Fortnightly | |---|---| | Car rego | $23 | | Car insurance | $31 | | Home insurance | $46 | | Council rates | $35 | | Christmas | $31 | | Car service | $15 | | Birthdays | $12 | | Holiday | $58 | | Total | $251/fortnight |

This is the amount you transfer to sinking funds every payday. Just like the bill account system, you transfer the same amount every pay, and the funds build up to cover the expenses when they arrive.

Step 3: Set up the accounts

Two approaches:

Option 1: One savings account with tracking

Keep all sinking funds in a single savings account, and track each fund separately in a spreadsheet or app. This is simpler and earns slightly more interest (larger balance), but requires you to track the allocation.

Option 2: Separate accounts for each fund

Open a savings account for each sinking fund. This is visually clear — the "Car Rego" account has exactly the car rego money — but it's more accounts to manage.

Most people start with Option 1 and move to Option 2 if they find themselves dipping into funds for other purposes.

Step 4: Automate the transfers

Set up an automatic transfer for the total per-pay contribution, timed for the day after payday. If you're using a single account, transfer the total. If you're using separate accounts, set up a transfer to each.

The key is automation — if you have to decide each pay whether to save, you'll find reasons not to. Automate it, and it happens.

Step 5: Track each fund

If you're using a single account, track each fund's balance in a savings tracker spreadsheet. For each fund:

• Target amount: what you need by the due date
• Current balance: how much is in the fund
• Per-pay contribution: how much you add each pay
• Due date: when you need the money
• On track?: whether the current balance and contribution rate will meet the target

Example tracker

| Fund | Target | Current | Per pay | Due | On track? | |---|---|---|---|---|---| | Car rego | $600 | $300 | $23 | Mar 2027 | Yes | | Christmas | $800 | $200 | $31 | Dec 2026 | Yes | | Holiday | $1,500 | $800 | $58 | Jul 2027 | Yes | | Car service | $400 | $50 | $15 | Jan 2027 | Behind |

The "Car service" fund is behind — at $15/fortnight, it won't reach $400 by January. You need to increase the contribution or add a lump sum.

Step 6: When the expense arrives

When a sinking fund expense arrives:

1. Check the fund balance — is there enough?
2. Pay the expense from the fund — transfer from savings to your everyday account, then pay
3. Reset the fund — if it's a recurring expense (rego, insurance), start building again for next year. If it's a one-off (a holiday), the fund is done.

If the fund is short

If the fund doesn't have enough (because the expense was higher than expected, or you started too late):

• Top up from the emergency fund if you have one
• Increase the contribution for the next cycle, so you're not short again
• Adjust the target if the expense is consistently higher than you estimated

Step 7: Review and adjust

Review your sinking funds quarterly:

• Are the targets accurate? If car insurance went up, update the target.
• Are you on track? If a fund is behind, increase the contribution.
• Are there new sinking funds to add? A new car, a child starting school, a planned move.
• Are there funds to remove? Expenses that no longer apply.

Common sinking fund mistakes

• Not having sinking funds at all. Without them, irregular expenses are a constant source of stress — you're always catching up. With them, the money is there.
• Mixing sinking funds with general savings. If you don't track separately, you'll spend the "car rego" money on a holiday and be short when rego is due.
• Underestimating the expense. If you budget $600 for car rego and it's $650, you're short. Use the actual amount from last year, and add a buffer.
• Starting too late. If rego is due in 2 months and you start saving now, you need to save $300/month instead of $50. Start as early as possible.
• Not adjusting for increases. Insurance, rego, and subscriptions go up. Review annually and update the contribution.
• Dipping into funds for other things. The "Christmas" fund is for Christmas, not for a new phone. If you dip in, you'll be short when Christmas arrives.

Sinking funds and the bill account system

Sinking funds work alongside the bill account system:

• Bills account: for regular, recurring bills (rent, phone, electricity)
• Sinking funds: for irregular, known expenses (rego, insurance, Christmas)
• Emergency fund: for unknown, unexpected expenses
• Savings goals: for specific targets (house deposit, holiday)

Together, these four cover every type of expense. The bills account handles the regular monthly costs. Sinking funds handle the irregular annual costs. The emergency fund handles the surprises. Savings goals handle the dreams.

When a spreadsheet isn't enough

A sinking fund spreadsheet is excellent for tracking, but it doesn't:

• Automatically calculate the per-pay contribution based on the due date — you have to do the maths.
• Alert you when a fund is behind — you have to check manually.
• Connect to your runway — to see whether your sinking fund contributions are affecting your everyday buffer.

The Payday Compass app handles all of this — enter each sinking fund with its target, due date, and contribution, and the app calculates the per-pay amount, tracks progress, and shows how the contributions affect your runway.

For a quick check on how much you can afford to put toward sinking funds, use the free payday calculator.

Summary

A sinking fund is money you set aside gradually for a known future expense. List your irregular expenses, calculate the per-pay contribution for each, set up a savings account (or track within one), automate the transfers, track each fund's balance, and pay the expense when it arrives. Sinking funds eliminate the stress of irregular costs — the money is there because you put it there in advance. Combined with a bill account, an emergency fund, and savings goals, sinking funds complete a household money system that covers every type of expense.

To track sinking funds with automatic runway connections, try the Payday Compass Goal Navigator.