Visual Summary
Calculator Inputs
Example Data Table
| Period | Taxable Sales | Sales Rate % | Taxable Purchases | Purchase Rate % | Import GST | Adj Output | Adj Input |
|---|---|---|---|---|---|---|---|
| 2026-01 | 2,500,000 | 18 | 1,700,000 | 18 | 80,000 | -12,000 | 5,000 |
| 2026-02 | 1,900,000 | 18 | 2,150,000 | 18 | 40,000 | 0 | 0 |
Formula Used
Input GST = Taxable Purchases × Purchase Rate
Net GST = (Output GST + Output Adjustments) − (Input GST + Import GST + Input Adjustments) − Prior Credits + Interest/Penalties
If Net GST < 0 → Refund = |Net GST|
If Net GST ≥ 0 → Payable = Net GST
How to Use This Calculator
- Choose currency and enter your tax period (YYYY-MM).
- Enter taxable sales and the applicable sales GST rate.
- Add zero-rated exports and exempt sales for turnover tracking.
- Enter taxable purchases and the purchase GST rate to estimate input tax.
- Include import GST paid and any adjustments (credit/debit notes, reversals).
- Enter any prior credits and interest/penalties, then submit.
- Review the refund/payable result shown above the form.
- Use CSV/PDF export to save your calculation history.
Saved Calculation History
| DateTime | Period | Currency | Output GST | Input GST | Import GST | Net | Refund | Payable |
|---|---|---|---|---|---|---|---|---|
| No history yet. Submit the form to add entries. | ||||||||
Refund and Payable Signals
A refund position appears when eligible input tax credits exceed output tax for the period. In the calculator, the net value becomes negative when input GST, import GST, and credit adjustments outweigh output GST. A payable position appears when output tax exceeds credits and adjustments, producing a positive net figure.
Inputs That Move the Outcome
\Taxable sales and the sales rate directly drive output GST, while taxable purchases and the purchase rate estimate input GST\. Import GST can materially increase credits in trading businesses\. Output adjustments capture debit and credit notes, and input adjustments capture reversals or additional claims\. Prior credits reduce the current net, while interest or penalties increase it\. For better precision, reconcile figures to invoice registers, exclude non\-creditable items, and separate capital goods where required\. Many businesses also compare current net to prior months to detect anomalies early internally\.
Export and Exempt Turnover Tracking
Zero-rated exports are included in turnover reporting but usually contribute little or no output GST. Exempt sales also increase turnover without output GST. Recording these values helps reconcile business activity to filings and supports internal review. Where rules require apportionment of credits for exempt activity, keep supporting schedules separately.
Using Adjustments for Accuracy
Adjustments exist because real invoices change. Enter credit notes as negative output adjustments to reduce output GST. Enter debit notes as positive output adjustments. For input adjustments, use positive numbers when reversing previously claimed credits, and negative numbers when adding additional eligible credits. These entries ensure the net position reflects corrected tax liability.
Reading the Charts
The current-period chart compares output GST against input-related components, including imports and adjustments, so you can see what drives the refund or payable outcome. The history chart plots net positions across saved runs. A consistent negative trend suggests recurring excess credits, while frequent swings can indicate timing effects or large adjustment events.
Recordkeeping and Exportable Reports
Download the CSV to keep a lightweight audit trail of your calculations, or export the PDF for sharing and review. Store invoice registers, customs documents, and credit note evidence alongside the report. Before filing, cross-check that rates match your tax category, that import credits are eligible, and that adjustments align with issued documentation.
FAQs
1) What does a negative net value mean?
A negative net indicates your credits exceed output tax for the period. The calculator reports this as a potential refund amount equal to the absolute net value.
2) Can I use different rates for sales and purchases?
Yes. Enter the sales rate for output GST and the purchase rate for input GST. This supports mixed-rate scenarios where purchases or supplies fall under different rate schedules.
3) How should I enter credit notes?
Enter credit notes as a negative output adjustment, because they reduce output GST. Use debit notes as positive adjustments when they increase output tax for the period.
4) What if some purchases are not creditable?
Reduce the taxable purchases amount to include only eligible inputs, or use an input adjustment to reverse ineligible portions. Always follow your local credit eligibility rules.
5) Does exempt turnover change the refund number?
Exempt turnover does not create output GST in the calculator, but it is tracked in turnover totals. If apportionment rules apply, adjust eligible input values accordingly.
6) What does the PDF/CSV export include?
Exports include your saved run history: key amounts, rates, net position, refund, and payable values. Use them as working papers alongside invoices and supporting documents.