Tony's never trusted a spreadsheet he didn't build himself, and after watching a few too many quotes come in with GST added, subtracted, or forgotten altogether, I don't blame him. Small jobs around the house, a bit of concreting, a new hot water system, a fence repair after the storms: all come with the same argument at the kitchen table. Is that price the tradie gave you including GST or not? You'd think after this many years someone would have made that clear on every invoice, but plenty still don't.
The maths itself isn't hard once you know which way you're going. To add ten percent GST to a price, multiply by 1.1. To find out how much GST is hiding inside a price that already includes it, divide by 11, not by 10, that trips more people up than anything else, because dividing by ten only works if you're finding ten percent of the total, not the GST component of a GST-inclusive figure. We've had actual disagreements over Sunday dinner about this, one of us insisting a $110 job has $10 of GST in it (correct) and the other briefly convinced it was $11 (also technically true if you're doing it the long way, but the shortcut of dividing by eleven gets you there in one step).
Rather than keep doing this on the back of a receipt or arguing about it, we use the GST calculator at https://freeonlinetools.au/tools/gst-calculator.php whenever a quote comes in. Type in the price, tell it whether GST is already included or needs adding, and it gives you both figures instantly, GST-exclusive and GST-inclusive, plus the GST component on its own. Handy when you're comparing two tradie quotes and one's quoted ex-GST out of habit while the other's quoted the final number, which happens more than you'd think, especially with smaller operators who aren't always consistent about how they present pricing.
It's also useful the other way around if you're doing cash work or selling something you built in the shed. If you've quoted a customer $500 for a job and that needs to include GST, you want to know straight away that your actual take is $454.55 with $45.45 going to the tax man, not find that out after you've already spent the lot on materials for the next job. Getting this backwards is a classic way small side hustles get themselves in strife with their numbers by tax time.
Where this connects to the bigger picture is household budgeting, because knowing the real cost of things, GST included, no surprises: is only half the job. The other half is knowing where it all fits against everything else going out the door each fortnight. We used to try tracking this in a notebook, then in a spreadsheet Tony built once and immediately regretted trying to update, and eventually gave up on both because neither of us actually kept it current. What we use now is the household budget planner at https://freeonlinetools.au/tools/household-budget-planner.php, mostly because it doesn't require opening a program, remembering a password to some app, or losing three months of data when a laptop dies.
The way we actually use it: every time a quote or invoice comes in for house stuff, plumbing, electrical, car rego, insurance renewals: we run it through the GST calculator first if the number's ambiguous, then log the real total into the budget planner against the right category. Doing it in that order means the budget's built on the actual cost of things rather than a rough guess that's out by whatever GST adds or doesn't add. Over a few months you start to see patterns you'd never catch doing it in your head: how much car running costs actually chew through compared to what you assumed, or that home maintenance always runs higher in the months after storm season because everyone's fixing the same roof damage at once.
The bit that actually keeps us using it rather than letting it lapse like every previous attempt is that it's quick enough to update standing at the kitchen bench with a receipt in hand, rather than something that needs a proper sit-down session on a Sunday night that never happens because there's always something more urgent. If it takes longer than making a cup of tea, it doesn't get done, that's just how it goes in a house with a workshop attached and always another job half-finished.
There's also the flip side of GST that catches people out in a different way, not every purchase has it. Basic fresh food, most medical costs, and a handful of other categories are GST-free, which means running every single household receipt through the calculator assuming ten percent is hiding in there somewhere will actually give you the wrong number for things like the weekly grocery shop. Worth knowing which categories are GST-free versus which aren't before you start assuming the calculator applies to absolutely everything that comes through the letterbox or the checkout.
Insurance renewals are another one worth double-checking every year rather than just renewing on autopilot. Home and contents, car, and even things like caravan insurance often arrive with a total that bundles GST, stamp duty and the base premium into one number, and working out the actual GST-exclusive premium lets you compare this year's renewal against last year's more honestly, rather than just looking at the bottom line and assuming a jump is all premium increase when some of it might be a stamp duty change on the government's end. We've caught a couple of quiet increases doing exactly this that would've slipped past if we'd just glanced at the total and paid it.
None of this is complicated stuff. It's basic arithmetic and basic tracking, but doing it consistently, with the right tools handling the parts that are easy to get wrong, is the difference between a rough idea of where the money's going and actually knowing. Tony still checks every GST calculation against his own mental maths out of habit, and so far the tool's been right every time, which either says something about the tool or something about thirty years of doing invoices the hard way finally paying off.
The maths itself isn't hard once you know which way you're going. To add ten percent GST to a price, multiply by 1.1. To find out how much GST is hiding inside a price that already includes it, divide by 11, not by 10, that trips more people up than anything else, because dividing by ten only works if you're finding ten percent of the total, not the GST component of a GST-inclusive figure. We've had actual disagreements over Sunday dinner about this, one of us insisting a $110 job has $10 of GST in it (correct) and the other briefly convinced it was $11 (also technically true if you're doing it the long way, but the shortcut of dividing by eleven gets you there in one step).
Rather than keep doing this on the back of a receipt or arguing about it, we use the GST calculator at https://freeonlinetools.au/tools/gst-calculator.php whenever a quote comes in. Type in the price, tell it whether GST is already included or needs adding, and it gives you both figures instantly, GST-exclusive and GST-inclusive, plus the GST component on its own. Handy when you're comparing two tradie quotes and one's quoted ex-GST out of habit while the other's quoted the final number, which happens more than you'd think, especially with smaller operators who aren't always consistent about how they present pricing.
It's also useful the other way around if you're doing cash work or selling something you built in the shed. If you've quoted a customer $500 for a job and that needs to include GST, you want to know straight away that your actual take is $454.55 with $45.45 going to the tax man, not find that out after you've already spent the lot on materials for the next job. Getting this backwards is a classic way small side hustles get themselves in strife with their numbers by tax time.
Where this connects to the bigger picture is household budgeting, because knowing the real cost of things, GST included, no surprises: is only half the job. The other half is knowing where it all fits against everything else going out the door each fortnight. We used to try tracking this in a notebook, then in a spreadsheet Tony built once and immediately regretted trying to update, and eventually gave up on both because neither of us actually kept it current. What we use now is the household budget planner at https://freeonlinetools.au/tools/household-budget-planner.php, mostly because it doesn't require opening a program, remembering a password to some app, or losing three months of data when a laptop dies.
The way we actually use it: every time a quote or invoice comes in for house stuff, plumbing, electrical, car rego, insurance renewals: we run it through the GST calculator first if the number's ambiguous, then log the real total into the budget planner against the right category. Doing it in that order means the budget's built on the actual cost of things rather than a rough guess that's out by whatever GST adds or doesn't add. Over a few months you start to see patterns you'd never catch doing it in your head: how much car running costs actually chew through compared to what you assumed, or that home maintenance always runs higher in the months after storm season because everyone's fixing the same roof damage at once.
The bit that actually keeps us using it rather than letting it lapse like every previous attempt is that it's quick enough to update standing at the kitchen bench with a receipt in hand, rather than something that needs a proper sit-down session on a Sunday night that never happens because there's always something more urgent. If it takes longer than making a cup of tea, it doesn't get done, that's just how it goes in a house with a workshop attached and always another job half-finished.
There's also the flip side of GST that catches people out in a different way, not every purchase has it. Basic fresh food, most medical costs, and a handful of other categories are GST-free, which means running every single household receipt through the calculator assuming ten percent is hiding in there somewhere will actually give you the wrong number for things like the weekly grocery shop. Worth knowing which categories are GST-free versus which aren't before you start assuming the calculator applies to absolutely everything that comes through the letterbox or the checkout.
Insurance renewals are another one worth double-checking every year rather than just renewing on autopilot. Home and contents, car, and even things like caravan insurance often arrive with a total that bundles GST, stamp duty and the base premium into one number, and working out the actual GST-exclusive premium lets you compare this year's renewal against last year's more honestly, rather than just looking at the bottom line and assuming a jump is all premium increase when some of it might be a stamp duty change on the government's end. We've caught a couple of quiet increases doing exactly this that would've slipped past if we'd just glanced at the total and paid it.
None of this is complicated stuff. It's basic arithmetic and basic tracking, but doing it consistently, with the right tools handling the parts that are easy to get wrong, is the difference between a rough idea of where the money's going and actually knowing. Tony still checks every GST calculation against his own mental maths out of habit, and so far the tool's been right every time, which either says something about the tool or something about thirty years of doing invoices the hard way finally paying off.
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