The estimate for a catch-up job is almost always built on one number: how many months are behind. Three months behind, quote three months of work. Six months, double it. It sounds fair right up until you open the file and realise the months were never the problem. What is inside them is. The scope of a catch-up job is not the size of the gap, it is the state of the data inside the gap, and that is the one thing you cannot see from the scoping call, which is exactly why the quote is almost always wrong.
Why the months-behind estimate breaks down
The first thing that blows the estimate is missing source documents. Bank statements with gaps, invoices that were never received, receipts the client swears exist but cannot locate: none of that surfaces during the initial call. It only appears once you are already inside the file, trying to reconcile a transaction with no paper trail behind it. Every gap becomes a conversation, then a chase, then a delay, and that is before a single GST code has been touched. The second thing is compounding, and it is the more expensive of the two. A bank rule that was miscoding transactions twelve months ago did not create one error, it created the same error every time that transaction type appeared, across every period since. Fixing it means correcting each instance and then checking whether those corrections ripple into BAS periods that have already been lodged. A single bad rule from eighteen months ago can turn a three-hour fix into a full day, and none of that is visible from the outside when you are building the quote.
The real time sink, though, is not volume at all. It is the decisions that unclear transactions force. Every transaction that could reasonably be coded two ways is a judgement call, and judgement calls are what actually slow the work down: mixed-use expenses, personal spending sitting in the business account, payments to related parties with no description, each one has to be investigated rather than simply categorised. GST errors that ripple forward are the other blowout that rarely gets priced in. If a client was on a cash basis while their previous bookkeeper coded accrual-style, or input tax credits were claimed on GST-free purchases across several quarters, fixing the current period is not enough. You have to work out which past BAS periods are affected, whether amendments are required, and whether the corrections change anything already lodged with the ATO. That work cannot be estimated from outside the file, because it depends entirely on what is in it.
Why the pricing model itself is the problem
Underneath all of this is one structural mistake: firms quote based on what the client describes, then price the hours it takes to do clean work on clean data. Catch-up data is never clean, so the quote is measuring the wrong thing from the start. The client's account of the situation is not a scope, it is a hopeful summary, and the gap between that summary and the actual file is where the unpriced hours live. This is not a client being difficult or a bookkeeper underquoting through carelessness. It is a genuine information problem: the person building the quote does not yet have the one input that determines the size of the job. Pricing confidently on a missing input guarantees the estimate is either padded to cover the unknown, which loses jobs, or optimistic, which absorbs the overrun. Neither is a good outcome, and both come from the same place.
How firms fix the estimate
The firms that get this right stop trying to quote the whole job blind and build an assessment step into the process instead. A paid or fixed-fee assessment phase, before the full quote, buys the one thing the scoping call cannot give: a look at the actual file. That is enough time to see what documents are missing, spot the recurring bank-rule errors that will compound, and check whether past BAS periods have been affected by whatever coding decisions were made along the way. It converts the biggest unknown in the job into a known before any fixed price is committed. Clients accept this far more readily than firms expect, because it is transparent and it protects them from a padded worst-case quote. Catch-up work blows out because the estimate is built on assumptions the data will disprove. The months behind are the starting point, not the scope, and the firms that separate assessing the job from pricing it quote more accurately, set expectations better, and stop quietly absorbing the cost of hours they never charged for.
