Fund Jars: Stop Getting Blindsided by Big Annual Bills

Every January, the car insurance renewal lands. Every December, Christmas arrives. Every spring, the boiler service is due. None of these are surprises, exactly, and yet they somehow still blow the monthly budget or end up on a credit card. The problem is not that people forget these bills are coming. The problem is there is nowhere to put the money in the meantime.

Fund Jars is a simple app built around a straightforward fix: give each irregular expense its own named jar, decide how much you need, pick a date, and start filling it. The app is fully offline, needs no account, and takes about two minutes to set up. The live version is embedded below, seeded with a handful of realistic jars so you can see immediately how it works.

The jar idea is not new, but most tools make it harder than it should be

Envelope budgeting has been around for decades. The idea is simple: allocate money to named categories before you spend it, and when the envelope is empty, you stop. The 'sinking fund' version of this applies the same logic to future spending, setting a little aside each month so a large bill does not arrive all at once.

Personal finance communities like r/UKPersonalFinance and MoneySavingExpert have written about this approach endlessly, because it genuinely works. The trouble is that most apps implementing it either require a bank connection, charge a monthly subscription, or bury the feature inside a broader budgeting system that takes hours to configure. Fund Jars does one thing: jars for irregular expenses, offline, with no account required.

Try it in the demo below. Tap any jar to see its progress, or hit the plus button to add your own.

What you actually see when you open it

The app opens on an overview screen with a handful of pre-filled jars: car insurance, holiday, Christmas, home repairs. Each jar shows a progress ring, a target amount, how much has been saved so far, and a simple verdict on whether the monthly contributions are on track. Green means you are ahead. Amber means you are close. Red means the monthly amount needs to go up.

The verdict is calculated from a straightforward sum: take what is left to save, divide by the number of months until the due date, and compare that required monthly figure against what you have actually been putting in. There is no algorithm involved. It is just arithmetic, shown clearly so you can act on it.

Tap into any jar and you see the full picture: a progress bar, a breakdown of contributions by month, and a chart showing the trajectory to the target. You can log a contribution in a few taps. The whole thing is stored locally on the device, nothing is sent anywhere.

Setting up a jar for your own bills

Creating a new jar takes about thirty seconds. Give it a name (car MOT, dog insurance, boiler cover, summer holiday, whatever applies to your life), enter the amount you need, and pick the month it is due. The app immediately tells you how much to set aside each month from today.

This is the part most people underestimate when they first try sinking funds: the required monthly figure is almost always smaller than the lump sum felt. A 600 pound car insurance renewal spread over twelve months is 50 pounds a month, which is much easier to absorb. The app makes that visible immediately, before you have even saved anything.

You can have as many jars as you need. Some people run four or five covering the main annual bills. Others build out fifteen or twenty covering everything from vet bills to birthdays. The app handles both comfortably, with a scrollable list and a summary bar at the top showing total saved across all jars and total monthly outgoing to stay on track.

Why offline and no-account matters

A lot of budgeting apps ask for a bank connection or at minimum an email address before they let you do anything. Fund Jars skips all of that. There is no login screen, no sync, no server. You open it and it works. Your data lives on your phone.

For a tool like this, that is the right call. Sinking fund tracking does not need real-time bank data. It needs you to record a monthly transfer into a savings pot, or even just a mental note that you moved the money. The discipline is the habit, not the automation. An app that gets out of the way and lets you build the habit is more useful than one that integrates deeply but adds friction.

The charts and breakdowns, visible in the screenshots, give you just enough feedback to stay motivated without turning the app into a dashboard you need to maintain. Monthly bar charts show the saved-per-month pattern over time. A category breakdown shows which parts of your life absorb the most sinking fund attention. These are the views that answer the questions people actually ask: am I saving consistently, and where does the money go.

Who this is built for

Fund Jars is aimed squarely at UK adults running a tight monthly budget who already know roughly what their big annual bills cost but have no structured way to prepare for them. It fits people who have tried spreadsheets but find them fiddly to maintain, and people who are curious about YNAB or Plum pockets but not ready to share bank access with a third-party app.

It works especially well for households where the bills are predictable in amount but irregular in timing: the annual renewal cycle that hits differently every month of the year, the holiday that needs booking in January for August travel, the Christmas budget that always somehow sneaks up regardless of how long it has been on the calendar.

If any of those situations sound familiar, the interactive demo above is worth five minutes of your time. Create a jar for your next big bill, put in the target and the date, and see what the required monthly figure actually is. It is almost certainly more manageable than the lump sum made it feel.