Key takeaways
What this article covers, in order:
- First, a word about guilt
- Step 1: Draw a line and stop the mess growing
- Step 2: Get every bank and card transaction in one place
- Step 3: Fix the opening balance
- Step 4: Triage before you categorise
- Step 5: Reconcile one month at a time, oldest first
A bookkeeping clean up goes in a particular order: freeze the mess, get every bank line in, fix the opening balance, then work forward month by month until each one reconciles. Skip the order and you'll fix the same transaction three times. Here's the seven-step plan we use, with a realistic example and an honest idea of how long it takes.
First, a word about guilt
Marcus runs a small independent gym in Cardiff. He opened in Jan 2026, kept the books beautifully for six weeks, and then got busy. By Oct 2026 he had a bank feed with around 1,100 uncategorised lines, a spreadsheet of memberships that stopped being updated in Apr 2026, and a shoebox (an actual shoebox) of equipment receipts.
He'd been avoiding it because looking at it made him feel bad. That's normal, and it's worth saying out loud: messy books are a time problem, not a character flaw. They're also very fixable. Nobody's books are too far gone if the bank statements exist.
Step 1: Draw a line and stop the mess growing
Before you fix the past, protect the present. Pick a date, usually the first of the current month, and from that day keep the books properly as transactions arrive. Categorise new lines weekly, raise invoices on time, enter bills as they come in.
This feels backwards. Surely you fix the old stuff first? No. If you start with the backlog, new mess piles up behind you while you work and you never catch up. Keeping today clean means the backlog is a fixed size, and it only gets smaller.
Step 2: Get every bank and card transaction in one place
Your bank statements are the backbone of the clean-up. Everything that happened to your money is on them.
- Connect your bank through Open Banking if you haven't already, so everything from today arrives on its own. Don't count on a new feed reaching back as far as your backlog does.
- For anything older, download CSV statements from online banking and import them.
- Don't forget credit cards, savings accounts and any payment-provider balances that pay out to your bank.
Then check for gaps. Put the closing balance of each statement next to the opening balance of the next one. If they don't agree, a statement is missing or a CSV was cut short.
Step 3: Fix the opening balance
Every clean-up depends on starting from a known, correct number. For a business that's been trading a while, that's usually the closing balance sheet from your last year-end accounts, prepared by your accountant. For a brand new business like Marcus's, the opening bank balance is whatever was in the account on day one (often zero, or whatever the owner paid in).
If you don't have a reliable starting point, ask your accountant. Getting this wrong means every reconciliation afterwards will be out by the same amount, and you'll waste hours hunting a difference that was baked in from the start.
Step 4: Triage before you categorise
Don't start at transaction one and work down. Sort first, then tackle the big, repetitive groups in bulk. It's quicker and you make fewer mistakes.
Here's roughly how Marcus's 1,100 lines broke down:
| Group | Lines | How to deal with it |
|---|---|---|
| Membership payments in | 620 | Categorise as sales in bulk; spot check a few |
| Rent, utilities, software subscriptions | 95 | Same supplier, same category every month: bulk |
| Equipment and supplies | 140 | Check against receipts, categorise individually |
| Transfers to savings and back | 38 | Record as transfers, not income or costs |
| Personal spending on the business card | 27 | Director's loan account (he trades as a limited company) |
| Refunds and reversals | 19 | Match to the original payment |
| Genuinely unknown | 161 | Park, then investigate in step 6 |
Look at that table. More than half the work was one group. Bulk handling of the obvious stuff gets most people 70 or 80 percent of the way in an afternoon.
Step 5: Reconcile one month at a time, oldest first
Now reconcile. Start with the earliest month, get it to agree with the statement, then move on.
Why one month at a time? Because a difference is far easier to find in 90 transactions than in 1,100. If Feb 2026 reconciles and Mar 2026 is £47.20 out, you know exactly where to look.
Common causes of differences during a clean-up:
- Duplicates. A line came in from both the feed and a CSV import. Delete one.
- Missing lines. A CSV was exported with the wrong date range.
- Opening balance wrong. See step 3.
- Transposed figures. £1,254 typed as £1,524. The difference (£270) divides by 9, which is the giveaway.
Once a month reconciles, lock it, and don't touch it again unless you have a good reason.
Step 6: Investigate the unknowns
This is the slow part, and there's no shortcut. For each unidentified transaction:
- Search your email for the amount and the date.
- Check your card or bank app, which often shows the merchant's full name.
- Ask whoever else uses the account.
- If it's a receipt in, check your invoices for a matching total.
Marcus got through 140 of his 161 unknowns this way in about three evenings. The remaining 21 small items, worth £318 in total, he couldn't identify at all. He parked them in a suspense account with a note, and his accountant decided how to treat them at year end. That's a perfectly acceptable outcome. Perfect is not the goal; honest is.
Step 7: Sort debtors and creditors, then hand over
Once the bank is clean, look at what's owed in each direction.
Debtors. Run the aged debtors report. Any invoice showing as unpaid that you know was paid hasn't been matched to its receipt, so match it. Anything genuinely unpaid and very old needs a decision: chase it, or talk to your accountant about writing it off.
Creditors. Same in reverse. Bills showing as unpaid that you know you paid need matching to the payment.
Finally, tell your accountant the books are clean and invite them in to look. A short note helps: the date you cleaned up to, anything left in suspense, and anything you weren't sure about.
How long does all this take?
It depends on volume, but for planning:
| Backlog | Rough time |
|---|---|
| 1 to 3 months, under 300 lines | One focused day |
| 4 to 9 months, 300 to 1,200 lines | Three to five sessions |
| A year or more | A week or two of evenings, or pay a bookkeeper |
There's no shame in paying a bookkeeper to do the clean-up and then keeping it tidy yourself afterwards. Often that's the most sensible use of your time.
How HelloBooks helps
You can connect your bank through Open Banking (most UK banks and cards) and import older history from CSV statements. Every transaction lands in a review list where you confirm or change the category. On Pro, AI categorisation suggests categories, which speeds up the bulk groups in step 4; when AI credits run out, AI categorisation pauses and the books keep working.
The bank reconciliation screen suggests a match for each statement line with a confidence score and the reason for the match, so you only work through the exceptions, and you can unmatch in one click. Each reconciled period can be locked, with reopenings logged. Your bookkeeper or accountant can be invited into the same books. There's more on the approach on our automated bookkeeping page.
FAQs
Should I fix old months or start fresh?
Do both, in that order of priority: keep the current month clean from today, then work through the backlog oldest first. Starting fresh without fixing the past leaves your year-end accounts unreliable.
What if I've lost some bank statements?
Most UK banks let you download several years of statements from online banking, or will send copies on request. Ask before assuming they're gone.
Can I just put everything I don't recognise in "general expenses"?
Please don't. It makes your profit wrong and hides personal spending. Park unknowns in suspense with a note, then investigate or ask your accountant.
Is it worth paying someone to clean up my books?
If the backlog is a year or more, often yes. A bookkeeper does it faster than you will, and you can take over once it's tidy.
How do I stop the mess coming back?
A short weekly session clearing the review list, plus a monthly reconciliation and lock. Small and regular beats big and occasional every time.
Start with step 1 today. Tomorrow's transactions are the easiest ones you'll ever categorise.
Start free, no card needed. Try HelloBooks Free
