What is a one-time purchase line in a budget?

It's a monthly budget category for small, unpredictable expenses like a tire repair, a broken kettle, or kids' boots bought mid-season. The specific expense is unpredictable, but the fact that something will come up each month is not.

Why not just use my emergency fund for small surprise expenses?

Frequent small withdrawals slowly drain the fund meant for job loss or major repairs, are rarely paid back, and make savings feel like a second chequing account. A dedicated line protects your emergency fund for real emergencies.

How much should I budget for one-time purchases each month?

Review six to twelve months of statements, total the small unplanned purchases, and divide by the number of months. Most households land between $100 and $300 a month. If you're unsure, start with $150 and adjust after three months.

What is the difference between a one-time purchase line, a sinking fund, and an emergency fund?

A one-time purchase line covers small, unpredictable, frequent costs. Sinking funds cover predictable irregular costs like annual insurance or holiday gifts. An emergency fund covers large, rare events like job loss or a new roof.

What should I do with unspent money in my one-time purchase line?

Let it roll over so you're covered in months with more than one surprise. Once it reaches a cap, such as three months' worth, sweep the extra into your TFSA, RRSP, or next savings goal.

13 Nov 2026 8 min read Advice

The One-Time Expense Fallacy And Why Your Budget Needs Room for Life’s Small Surprises

If you've been following my monthly budget updates, you may have noticed a pattern. Almost every month, I write some version of the same sentence - we would have come in lower if it weren't for one thing.

One month, it was a last-minute plane ticket for a family member to go see a relative who was sick. There was no time to shop around for a better fare, and no question of whether we'd pay it.

Another month, a rock got wedged between the rotor and pad on one of our cars' rear brakes. The brake seized, the rock ground into the rotor, and the pad cracked.

Then we had to replace the exhaust on one of our cars. Not a muffler or a pipe, but the entire system.

And this summer, we signed one of our kids up for a summer camp and prepaid for the whole season. He hated it. The camp was non-refundable, but making him spend his summer miserable wasn't an option, so we moved him to a different camp that he loved and paid for that one too.

Four months, four completely unrelated expenses. A couple were bigger than I'd like, but none were roof-sized, and none could have been predicted. Yet every month had one.

That's what led to this post. If something comes up every single month, it isn't really unexpected. It's a regular expense that looks different each time. And if your budget can handle it, it deserves its own line - a "one-time purchase" line, or a buffer. Whatever you call it, you need a bit of cushion.

Every Month Has a One-Time Expense

Here's the shift in thinking that makes this work - the specific expense is unpredictable, but the existence of an expense is not.

You don't know whether this month will bring a nail in your tire, a coffee pot that slips out of your hand, or a last-minute birthday gift for a party on Thursday. You do know that something will come up. Look back at any three months of bank statements and you'll find them between the groceries and the hydro bill.

Budget as if these won't happen and your plan only works in a month where nothing breaks. That month is rare.

Why You Shouldn't Just Use Your Savings

"That's what my emergency fund is for." I hear that and I get it. But there are a few problems with pulling from savings for small, routine surprises.

It slowly drains the fund meant for real emergencies. An emergency fund is there for job loss, a major car repair, or a sudden move. Dip into it for $80 here and $150 there and the balance creeps down until, when something big happens, it's not all there.

Refilling it rarely happens. You'll put the $200 back "next month." Then next month has its own surprise.

It breaks the habit of saving. When money is constantly going in and out, savings starts to feel like a second chequing account, and the next withdrawal gets easier to justify.

It makes you feel like you failed when you didn't. When a $60 expense "breaks" your budget, it feels like you did something wrong. Do that enough times and budgeting starts to feel like something you're bad at. In reality, the budget was just missing a line.

A one-time purchase line fixes all of this. The tire, the coffee maker, the boots - they're all planned for, so paying for them is just the budget doing what it's supposed to do.

What Belongs in This Line

The one-time purchase line is for small to mid-sized things that are unplanned but not catastrophic. A good rule of thumb - if it's annoying but doesn't change your month, it goes here. Some examples from experience:

Car stuff - a tire repair or single replacement tire, a dead battery, wiper blades that gave out in a snowstorm, a boost or a tow from a parking lot, a cracked side mirror. If you are fortunate and have more than one car, the costs to maintain all creep up.

Around the house - a broken coffee maker (happened twice last year and we eventually went back to manual coffee making), toaster, or blender. A toilet seat. A burned-out bulb in a fixture that takes a specialty bulb (this happened to me as soon as I started writing a draft of this post. The absolute cheapest replacement I can find locally is $21 on sale…$36 regular price.). Smoke detector batteries, or the detector itself when it hits its expiry date and won't stop chirping.

Kids - shoes or boots they outgrew mid-season, a field trip or class fee that showed up in their backpack, a birthday gift for a classmate's party, a replacement water bottle (eventually we bought two expensive, durable ones), a broken lunch bag zipper. With two young kids at home, I can confirm this category alone justifies the line. Some months are easily $400-$500 over the budget.

Tech - cracked cable (ended up buying USB-C cables in bulk), a cracked screen protector, a new remote because the kids dropped it in a cup of water (twice it happened by the way in the last 2 years).

Health and personal - a prescription that isn't fully covered, new reading glasses, a replacement retainer, you slept funny and now you need a massage and a visit to a specialist.

They're too small to treat as emergencies and too frequent to ignore.

What Doesn't Belong

Knowing what this line isn't for keeps it from becoming a catch-all.

Big repairs and replacements - A new roof, a furnace, a transmission, or a major dental procedure are too large for a monthly line. These belong in your emergency fund or a dedicated long-term savings account.

Predictable irregular expenses - Your annual car insurance, property tax installments, Costco membership renewal, holiday gifts, and back-to-school shopping aren't surprises. You know they're coming and roughly what they'll cost. These belong in sinking funds, where you set aside a fixed amount each month for a specific known expense. Our budget includes monthly fractional amounts that add up to the total payment when it is due.

Wants dressed up as needs - "My headphones still work, but the new ones are really good" is fun money, not a one-time purchase.

Here's a simple way to think about the three layers:

One-time purchase line - small, unpredictable, frequent. Tires, kettles, boots.
Sinking funds - predictable, irregular, known in advance. Insurance, gifts, memberships.
Emergency fund - large, unpredictable, rare. Job loss, roof, major car repair.

How Much Should You Set Aside?

The best number comes from your own history. Go through your last six to twelve months of bank and credit card statements and flag every purchase that fits the categories above. Add them up and divide by the number of months. That's your baseline.

I wouldn’t be surprised if this lands between $200 and $500 a month. A single person in an apartment with no car sits at the low end; a family with kids, a house, two vehicles, and a dog sits at the high end or above. No time for statements? Start with $150 and adjust after three months.

Based on our past statements, we need about $400. A catch-all category doesn’t quite work for us so we bumped a few of the existing categories by a portion of the $400. Children expenses went up by $150, car maintenance up by $150, general spending up by $100.

Once the line builds a balance, it can absorb mid-sized hits like our exhaust or the second camp. Anything bigger belongs to the emergency fund.

Rules That Make It Work

Let unspent money roll over - Some months nothing breaks. Don't spend the leftover; next month might bring two surprises at once.

Set a cap, then sweep the extra - Once the balance reaches a set amount, say three months' worth, send anything above it to your TFSA, RRSP, or whatever your next savings priority is. This keeps the line from becoming a pile of idle cash.

Keep it separate - Many Canadian banks and online banks let you open free sub-accounts or label savings "buckets." A labelled account keeps it from blending into daily spending.

Track what you use it for - A quick note in your budgeting app or spreadsheet is enough. After a year, patterns appear. If you're replacing a $30 kettle every eight months, a better kettle might be the smarter buy. This is how I can see what I unexpectedly spent $500 on several years ago.

Fix before you replace - Sometimes the cheapest one-time purchase is no purchase at all. A broken knob, clip, or bracket can often be fixed with a part ordered online, or in my case, printed on a 3D printer for a few cents. The line is there to absorb costs, not to encourage replacing things by default.

What If You Can't Afford It Right Now?

This line comes with an honest caveat - it's for people who have room in their budget. If every dollar is already committed to rent, food, and debt payments, a $200 line isn't realistic, and that's okay.

Even then, start small. Twenty-five dollars a month is $300 a year. That's a tire repair, a kettle, and a pair of kids' boots you didn't have to put on a credit card at 20% interest.

I started this way as a student. I kept $20 in a desk drawer for small one-off emergencies (petty cash if you will) and slowly added loose change and the odd $5 bill. One day my car radio died, and the drawer covered a $65 used replacement. My savings account, meant for bigger things like a set of new tires, stayed untouched.

A small buffer beats none, and you can grow it as your situation improves.

The Real Benefit

The bigger benefit is how it changes your relationship with your budget. When the coffee pot breaks, you don't panic or feel guilty. You just buy a new one, because you already planned for it.

That's what a good budget does. It doesn't pretend life is predictable. It plans for the fact that it isn't.