Bookkeeping Calculator

GST Calculator (Australia)

Add GST to a price, take GST off a GST-inclusive price, or find how much GST is in a total. Australian rate: 10%.

Bookkeeping Formula Reference

Every formula used by these calculators. They match the FNSACC323 Perform financial calculations unit.

Tax
GST: Add
Price inc GST = Price ex GST × 1.1
e.g. $100 × 1.1 = $110
GST: Remove
Price ex GST = Price inc GST ÷ 1.1
e.g. $110 ÷ 1.1 = $100
GST: Find Amount
GST = Price inc GST ÷ 11
e.g. $110 ÷ 11 = $10
Business
Markup
Selling Price = Cost + (Markup% × Cost)
e.g. Cost $50, Markup 20% → SP = $50 + ($50 × 0.20) = $60
Profit Margin
Selling Price = Cost ÷ (1 − Margin%)
e.g. Cost $50, Margin 20% → SP = $50 ÷ 0.80 = $62.50
Sales Commission
Commission = Rate% × Total Sales
e.g. $10,000 sales at 5% → Commission = $500
Simple Interest
Simple Interest
Interest = Principal × Rate × Number of Periods (T)
I = P × R × T
e.g. $300 at 2% for 1 year → I = $300 × 0.02 × 1 = $6
Total Value / Total Repayable
Total = Principal + Interest
e.g. $300 + $6 = $306
Compound Interest
Future Value (Compound)
FV = PV × (1 + i/n)^(n×t)
PV = present value, i = annual rate, n = periods/year, t = years
Present Value
PV = FV × (1 + i/n)^(−n×t)
How much to invest now to reach a future target
Loan Repayment
Repayment = P × [rp × (1 + rp)^N] ÷ [(1 + rp)^N − 1]
rp = rate per period, N = total periods
Depreciation
Straight Line: No Residual
Depreciation = Total Cost ÷ Effective Life
e.g. $11,000 ÷ 5 yrs = $2,200 per year (same each year)
Straight Line: With Residual
Depreciation = (Total Cost − Residual) ÷ Effective Life
e.g. ($11,000 − $1,000) ÷ 5 = $2,000 per year
Diminishing Value: Rate
Rate % = 200% ÷ Effective Life
e.g. 200 ÷ 12 yrs = 16.67%
Diminishing Value: Depreciation
Depreciation = Rate % × Carrying Amount
Applied to the reducing book value each year, bigger early, smaller later

GST Calculator (Australia)

GST Rate: 10%
$

Results

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Markup / Profit Margin

Markup calculates profit as a percentage of the cost price. Profit Margin calculates profit as a percentage of the selling price.

SP = Cost + (Markup% × Cost)
$
%

Results

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Sales Commission

Commission = Rate% × Total Sales
$
%
$

Results

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Break-Even Point

Units = Fixed Costs ÷ (Price − Variable Cost)

Fixed Costs stay the same no matter how much you sell (e.g. rent, insurance). Variable Cost is what it costs to make or deliver one single unit (materials, packaging, per-item shipping) — it goes up and down with sales, unlike fixed costs. Selling Price is what you charge per unit.

$
$
$

Results

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Simple Interest

I = P × R × T
$
%

Results

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Compound Interest

FV = PV × (1 + I)ᴺ
$
%
$

Results

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Present Value

PV = FV × (1 + I)⁻ᴺ
$
%

Results

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Depreciation

Depn = (Cost − Residual) ÷ Life
$
$

Results

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Time to Decimal

Decimal Hours = Hours + (Minutes ÷ 60)
hrs
min

Results

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Pay Calculator (Before Tax)

Gross Pay = (Rate × Ord. Hours) + (Rate × OT × OT Hours)
$

Results

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GST / VAT / Sales Tax Calculator

Rate: 15%
%
$

Results

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How to calculate GST

GST in Australia is 10% of the price before GST. That gives three formulas, depending on which number you start with.

Add GST

Price inc GST = Price ex GST × 1.1

Remove GST

Price ex GST = Price inc GST ÷ 1.1

Find the GST in a total

GST = Price inc GST ÷ 11

Example. A tradie quotes $800 plus GST. The invoice total is $800 × 1.1 = $880, and the GST is $80.

Going the other way, a receipt shows $880 including GST. The GST is $880 ÷ 11 = $80 and the price before GST is $880 ÷ 1.1 = $800.

The common mistake

Taking 10% off a GST-inclusive price does not remove the GST. 10% of $880 is $88, which would leave $792, not $800. GST is one eleventh of the total, not one tenth, because the total is already 110% of the original price.

Who has to charge GST

You must register for GST when your business has a GST turnover of $75,000 or more ($150,000 or more for non-profit organisations). Taxi and ride-share drivers must register whatever they earn. Some things are GST-free, including most basic food and some health and education services. The ATO’s GST pages have the full rules.

Frequently asked questions

How do I work out the GST from a total price?

Divide the GST-inclusive total by 11. For a $110 total, the GST is $110 ÷ 11 = $10.

Is GST 10% of the total price?

No. GST is 10% of the price before GST, which works out to one eleventh of the GST-inclusive total.

How do I add GST to a price?

Multiply the GST-exclusive price by 1.1. A $100 price becomes $110 including GST.

When do I need to register for GST?

When your GST turnover is $75,000 or more, or $150,000 or more for non-profit organisations. Taxi and ride-share drivers must register regardless of turnover.

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