# Calculator methodology and sources

Source: https://calculatax.com/methodology/
Title: How Our Calculators Work: Methodology & Sources | Calculatax
Last updated: 2026-11-07

Every one of our [Australian tax & pay calculators](https://calculatax.com/) applies published formulas for the 2026-27 financial year (1 July 2026 to 30 June 2027). Rates come from the Australian Taxation Office (ATO), the Fair Work Ombudsman, the ABS, Services Australia and the Department of Social Services, last checked on 1 November 2026.

## Where our rates come from

We take each figure from the official page that publishes it and record the page and the date we checked it. [About Calculatax](https://calculatax.com/about/) explains who runs the site and how to report an error.

| Calculator family | Source |
|---|---|
| Income tax rates | [ATO resident rates](https://www.ato.gov.au/tax-rates-and-codes/tax-rates-australian-residents), confirmed against the ATO new-legislation page |
| Low income tax offset | ATO LITO page |
| Medicare levy | ATO low-income thresholds and the Medicare Levy Act 1986 |
| HELP and other study loans | [ATO repayment thresholds](https://www.ato.gov.au/tax-rates-and-codes/study-and-training-loan-minimum-repayment-income-and-rates) |
| PAYG withholding | [ATO Schedule 1 coefficients](https://www.ato.gov.au/tax-rates-and-codes/payg-withholding-schedule-1-statement-of-formulas-for-calculating-amounts-to-be-withheld/coefficients-to-use-in-formulas-for-withholding-from-weekly-payments), applying to payments from 1 July 2026 |
| Super | [ATO super guarantee](https://www.ato.gov.au/tax-rates-and-codes/key-superannuation-rates-and-thresholds/super-guarantee) and contribution caps pages |
| Minimum wage | Fair Work Commission decision and Fair Work Ombudsman release, 1 July 2026 |
| Earnings statistics | ABS Average Weekly Earnings and Employee Earnings releases |
| Age Pension age, rates and deeming | Services Australia; Department of Social Services payment rates lists |
| Super balances and life expectancy | ATO taxation statistics 2023-24; ABS life tables |
| GST | [ATO GST page](https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/goods-and-services-tax-gst) |

*Sources for 2026-27 rates, checked 1 November 2026.*

## Calculation methods by calculator family

### Income tax and offsets

Resident income tax is the base amount for the bracket plus the marginal rate on each dollar above its lower threshold.

| Taxable income | Tax |
|---|---|
| $0 to $18,200 | Nil |
| $18,201 to $45,000 | 15c for each $1 over $18,200 |
| $45,001 to $135,000 | $4,020 plus 30c for each $1 over $45,000 |
| $135,001 to $190,000 | $31,020 plus 37c for each $1 over $135,000 |
| $190,001 and over | $51,370 plus 45c for each $1 over $190,000 |

*2026-27 resident rates. Source: ATO.*

Net tax is income tax, minus LITO, plus the Medicare levy, plus any HELP repayment.

### How LITO and the Medicare levy are applied

The low income tax offset (LITO) is $700 up to $37,500. It falls by 5c per $1 from $37,501 to $45,000, leaving $325. It then falls by 1.5c per $1 above $45,000 and reaches nil at $66,667.

LITO is non-refundable, so we cap it at the income tax payable.

The Medicare levy is 2% of taxable income. Above the low-income threshold, we apply the shade-in rule: the levy is the lower of 2% of income and 10c for each $1 above the threshold.

We use the latest announced thresholds, which are for 2025-26: $28,011 for singles, $47,238 for families plus $4,338 per child, and $44,268 for single SAPTO recipients. At $30,000, the levy is $198.90 under the shade-in.

### PAYG withholding

Withholding follows the ATO Schedule 1 formula y = ax − b. Here x is weekly earnings in whole dollars plus 99 cents, and a and b are the [ATO Schedule 1 coefficients for weekly payments](https://www.ato.gov.au/tax-rates-and-codes/payg-withholding-schedule-1-statement-of-formulas-for-calculating-amounts-to-be-withheld/coefficients-to-use-in-formulas-for-withholding-from-weekly-payments) for the earnings band and scale. We round y to the nearest dollar, with 50 cents rounded up, as the ATO formula rules require.

Other pay cycles convert to and from a weekly figure:

- Fortnightly: halve the earnings, find the weekly withholding, then double it.
- Monthly: add 1 cent if the amount ends in 33 cents, multiply by 3 and divide by 13. Multiply the weekly withholding by 13, divide by 3, and round to the nearest dollar.
- Quarterly: divide the earnings by 13, then multiply the weekly withholding by 13.

### Worked example: $6,500 a month on Scale 2

$6,500 a month on Scale 2 (tax-free threshold claimed) converts to x = $1,500.99. Then y = 0.3200 × 1,500.99 − 181.7319 = $298.58, rounded to $299. Monthly withholding is $299 × 13 ÷ 3 = $1,296.

### HELP repayments

HELP and other study loan repayments use the 2026-27 marginal system. Nothing is repaid up to $69,528. Above that, it's 15c per $1 to $129,717, then $9,028 plus 17c per $1 to $186,050.

Above $186,050, the repayment is 10% of total repayment income, including the first $186,050. Withholding for study loans uses the ATO Schedule 8 formula in the same y = ax − b form.

### Super

Super guarantee is 12% of qualifying earnings, up to the annual maximum contribution base of $270,830. Contribution cap checks use $32,500 concessional and $130,000 non-concessional.

Division 293 applies above $250,000. The co-contribution matches 50c per $1 up to $500, falling evenly to nil between $49,293 and $64,293.

### GST

Adding GST multiplies the GST-exclusive price by 1.1. Removing it divides the GST-inclusive price by 11 to find the GST. On a BAS, GST on sales (1A) is taxable sales including GST ÷ 11, and GST credits (1B) are claimable purchases including GST ÷ 11.

## Rounding and assumptions

Annual tax figures are worked out to the cent. Withholding amounts are whole dollars, as set out above. Take-home pay per period divides the annual result by 12, 26 or 52.

Unless you change an input, each calculator assumes:

- You're an Australian resident for tax purposes for the whole year.
- The income you enter is your taxable income, with no other income.
- You pay the Medicare levy at the single rate and have no exemption.
- You have no HELP debt and no Medicare levy surcharge to pay.

## What our calculators do not model

Results are estimates, as our [Disclaimer](https://calculatax.com/disclaimer/) sets out, and will differ from your notice of assessment when any of these apply:

- Part-year residency, foreign income or capital gains.
- Tax offsets other than LITO, and SAPTO outside the SAPTO calculator.
- Franking credits, business income and PAYG instalments.
- Termination payments, lump sums and other payments taxed under special rules.
- Medicare levy exemptions and private health insurance rebates.

Some 2026-27 figures are not yet published. The Medicare levy low-income thresholds and the SAPTO table use the latest published 2025-26 values until the ATO confirms new ones.

The working-from-home fixed rate for 2026-27 is not yet confirmed. The working Australians tax offset (WATO) starts in 2027-28, so it's not in 2026-27 results.

## Version history

The [changelog](https://calculatax.com/changelog/) lists rate and rule changes, with their pages and sources.

- [About Calculatax](https://calculatax.com/about/)
- [Disclaimer](https://calculatax.com/disclaimer/)
- [Privacy policy](https://calculatax.com/privacy/)
- [Terms of use](https://calculatax.com/terms/)

## Sources

- [ATO: Tax rates for Australian residents](https://www.ato.gov.au/tax-rates-and-codes/tax-rates-australian-residents)
- [ATO: Study and training support loans rates and repayment thresholds](https://www.ato.gov.au/tax-rates-and-codes/study-and-training-loan-minimum-repayment-income-and-rates)
- [ATO: Schedule 1 coefficients](https://www.ato.gov.au/tax-rates-and-codes/payg-withholding-schedule-1-statement-of-formulas-for-calculating-amounts-to-be-withheld/coefficients-to-use-in-formulas-for-withholding-from-weekly-payments)
- [ATO: Super guarantee](https://www.ato.gov.au/tax-rates-and-codes/key-superannuation-rates-and-thresholds/super-guarantee)
- [ATO: Goods and services tax (GST)](https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/goods-and-services-tax-gst)