BAS preparation is the process of verifying and collating a client's GST-coded transaction records for a given period, calculating the net GST position, and submitting the completed Business Activity Statement to the ATO. For accounting practices managing multiple clients, the quality of BAS preparation depends less on the work done on lodgement day and more on the discipline maintained throughout the period.
This checklist is structured in four stages: practice setup, period-open, pre-lodgement review, and post-lodgement. Following it consistently means lodgement day is a confirmation, not a discovery.
All ATO thresholds, dates, and obligations referenced below are drawn from current ATO guidance. Always confirm at ato.gov.au before applying to a specific client situation.
Stage 1: Practice setup (once per client onboarding)
The following setup tasks reduce ongoing BAS preparation time for every period. Done once correctly, they persist across quarters.
1.1 Configure coding rules for recurring vendors
Every client has a set of recurring vendors that appear on the bank statement every period: payroll providers, utilities, software subscriptions, insurance, rent. Map each one to the correct account code and GST code before the first statement arrives.
In Reconlink, coding rules are managed per client in Settings → Coding Rules. A rule specifies a vendor pattern, the account code to assign, and the GST code. When a transaction matches the pattern, it is coded automatically — the bookkeeper reviews rather than re-codes.
GST codes to configure:
- GST — standard rated taxable supply (most business purchases with 10% GST)
- FRE — GST-free (basic food, health, exports, certain educational services)
- INP — input-taxed (bank fees, merchant fees, residential rent)
- N-T — not taxable / out of scope (ATO payments, government charges, ASIC fees, super contributions)
- CAP — capital purchase (depreciable assets, hitting G10 rather than G11)
See our GST coding guide for the correct treatment of common Australian vendor categories.
1.2 Set the BAS frequency and period dates
Confirm whether the client lodges quarterly or monthly. The standard quarterly dates per the ATO BAS due dates page:
| Quarter | Period | Standard due date |
|---|---|---|
| Q1 | 1 Jul – 30 Sep | 28 October |
| Q2 | 1 Oct – 31 Dec | 28 February |
| Q3 | 1 Jan – 31 Mar | 28 April |
| Q4 | 1 Apr – 30 Jun | 28 July |
BAS and tax agents registered under the BAS agent lodgement program receive a further four-week extension. Confirm the current program dates with the ATO each year.
1.3 Set up the bank feed or import method
Determine how transactions will reach the ledger for each client:
- Direct bank feed — if the client's bank supports Basiq CDR, connect via Reconlink's bank feed integration. Transactions arrive automatically; no CSV downloads required.
- Bank statement email — if the client forwards bank statements by email to their Reconlink inbox address, the per-client email inbox auto-imports the attachment. Supported formats: CSV, Excel, PDF (major AU banks).
- Manual CSV upload — for banks not yet on the CDR network, download the statement from internet banking and import via the statement import tool.
1.4 Create a period lock discipline
Agree with the client (or establish a practice policy) that no transactions will be back-dated into a reconciled period. In Reconlink, locking a reconciled period via Reconciliations → Lock period prevents back-dated entries from silently changing the GST position after lodgement.
Stage 2: Period-open tasks (first week of each new quarter)
2.1 Confirm the opening bank balance
Reconcile the opening balance of each bank account against the closing balance from the previous period. Any discrepancy means the prior period has an unresolved item and must be corrected before the new quarter begins.
2.2 Review the client's payroll configuration (if applicable)
For clients with employees, confirm:
- Single Touch Payroll (STP) is enabled and reporting correctly for the period
- W1 (Total salary, wages and other payments) on the BAS will match the STP YTD total for the quarter
The ATO cross-checks W1 against STP data. A mismatch generates an ATO query. The safest approach is to run the cross-check yourself before lodgement rather than after.
2.3 Import or sync outstanding bank transactions
Run the bank feed sync or import the period's bank statements at the start of the quarter rather than at the end. Earlier imports mean more time for coding rule matches to process and more opportunity to catch anomalies before lodgement week. For practices using AI-assisted coding, see How AI is changing bookkeeping in Australia for guidance on evaluating auto-code accuracy and setting appropriate confidence thresholds.
Stage 3: Pre-lodgement review (one to two weeks before due date)
This is the most time-sensitive stage. For multi-client practices, work through each client in order of lodgement deadline.
3.1 Verify all transactions are coded
In Reconlink's transaction coding view, filter by "Uncoded" to confirm every bank feed transaction for the period has been assigned both an account code and a GST code. Any uncoded transactions inflate the manual review queue and make the BAS figures unreliable until cleared.
3.2 Audit GST coding on the top-20 vendors
Pull the top 20 vendors by spend for the quarter. For each, confirm:
- The GST code is consistent with the prior quarter
- The treatment matches the ATO's classification for that vendor type
- Any new vendor that appeared this quarter has been correctly coded
The 80/20 of BAS errors comes from the top 20 vendors. The long tail (vendors with one or two transactions per year) is less likely to cause a material misstatement.
3.3 Check capital purchases
Any purchase intended as a depreciable asset must be coded CAP (hitting G10) rather than as an operating expense. Key checks:
- Items above the instant asset write-off threshold for the 2025–26 income year ($20,000 for businesses with turnover under $10 million; assets first used or installed ready for use between 1 July 2025 and 30 June 2026) must go to the general pool, not be written off in full
- Items under the threshold can be claimed in full; confirm the CAP code is correctly applied so G10 is populated
3.4 Reconcile every bank account to the source statement
Run the bank reconciliation for each account before generating the BAS. An unreconciled balance means the G-label figures are based on unverified transactions. Reconlink's reconciliation engine surfaces unmatched items for each account and blocks period close until the balance is zero. For a step-by-step explanation of the reconciliation process itself, see What is bank reconciliation? A guide for Australian bookkeepers.
3.5 Run the W1 / STP cross-check
For clients with payroll: pull the STP YTD wages report for the quarter from the payroll platform and compare the total to W1 on the draft BAS. Investigate any material difference at the payroll source before lodging — never adjust W1 manually to match an incorrect STP figure.
3.6 Generate and review the BAS worksheet
Once all coding and reconciliation is clean, generate the BAS in Reconlink's BAS worksheet view. Review each G-label:
- G1 (total sales) should match total turnover for the period
- G9 = G8 ÷ 11 — the GST collected on taxable sales
- G20 = G19 ÷ 11 — the GST credits on eligible purchases
- Net GST = 1A (G9) minus 1B (G20)
A net GST figure that looks materially different from prior quarters (without a known reason) is worth investigating before lodgement. Common causes: a large capital purchase (increases 1B), a new revenue stream with a different GST treatment (affects G3/G4), or a one-off export (shifts G1 to G2).
Stage 4: Post-lodgement tasks
4.1 Lock the reconciled period
Immediately after lodgement, lock the period in Reconlink. This prevents any transaction — including correcting journal entries — from being back-dated into the lodged quarter without a deliberate override.
4.2 File the lodgement confirmation
Store the ATO lodgement reference number against the client record. For practices using tax agent software, the lodgement receipt is automatically retained; for manual lodgements, capture the confirmation email.
4.3 Note any post-lodgement corrections for next quarter
If a coding error or missing transaction is discovered after lodgement, record it now rather than trying to reconstruct it at the end of the next quarter. Reconlink's audit log captures every coding change with a timestamp and the user who made it — use it to trace the origin of corrections.
4.4 For material errors: lodge an amended BAS
If the post-lodgement correction changes the net GST position by more than a material threshold, consider lodging an amended BAS through the ATO's online amendment process. For smaller corrections, the ATO allows the net difference to be absorbed into the next BAS period — confirm the current threshold with the ATO before deciding which approach to take.
Checklist summary
Setup (once per client)
- Coding rules configured for recurring vendors
- BAS frequency and period dates set
- Bank feed or import method established
- Period lock policy agreed
Period-open
- Opening balance verified against prior period close
- Payroll / STP configuration confirmed
- Transactions imported or synced
Pre-lodgement review
- All transactions coded (zero uncoded)
- Top-20 vendors audited for GST code consistency
- Capital purchases reviewed against write-off threshold
- All bank accounts reconciled to source statements
- W1 / STP cross-check completed (if payroll applies)
- BAS worksheet reviewed and G-labels validated
Post-lodgement
- Period locked in reconciliation tool
- Lodgement reference filed
- Any corrections noted for next quarter
- Amendment lodged if correction is material
Frequently asked questions
How far in advance should BAS preparation start? For a quarterly BAS with a standard 28-day due date, begin the pre-lodgement review at least 10 business days before the deadline. Multi-client practices typically open the process for the largest clients two weeks before and work through the cohort in deadline order. Leaving BAS preparation to the final two days creates time pressure that increases the chance of errors.
What is the penalty for lodging an incorrect BAS in Australia? The ATO applies a Failure to Lodge (FTL) penalty for late lodgement, calculated per penalty unit (currently $330 per unit from 1 July 2023). For an incorrect BAS that underpays GST, the ATO may also apply a Shortfall Amount and General Interest Charge (GIC). Registered BAS agents who lodge incorrect statements may face additional professional consequences under the Tax Agent Services Act 2009. Always confirm current penalty rates at ato.gov.au.
What is the difference between a BAS agent and a tax agent? A BAS agent is registered with the Tax Practitioners Board (TPB) to provide BAS services, including preparing and lodging BAS statements on behalf of clients. A tax agent is registered to provide a broader range of tax agent services, including income tax returns. Both must meet CPE requirements and professional indemnity insurance obligations. For practices providing only bookkeeping and BAS services, BAS agent registration is the relevant credential.
Can Reconlink generate a BAS-ready worksheet automatically? Yes. Once all transactions for a period are coded and the bank accounts are reconciled, Reconlink's BAS worksheet feature calculates and populates all G-labels automatically using the ÷11 rule for GST calculations. The worksheet can be exported for review before lodgement. Reconlink does not lodge directly with the ATO — lodgement is completed through your tax agent software or the ATO's business portal.
How should a practice handle a client who provides transactions late? Set a cutoff date (typically 5–7 business days before the BAS due date) after which no new transactions will be incorporated into the current quarter's BAS. Communicate this cutoff in writing to clients at the start of each period. Late transactions go into the next quarter unless they materially change the GST position, in which case evaluate whether an amended BAS is warranted.
This checklist was last reviewed against ATO guidance on 22 May 2026. BAS due dates, penalty rates, and write-off thresholds change — always confirm current figures at ato.gov.au. This is general guidance, not specific tax advice.