How to get tax calculation right
This is one of those topics that looks small until it costs you something. The short answer to tax calculation is that it is mostly a sequence of small decisions, not one big one.
Small percentage changes matter here because they apply to every order, every month. Check it against what you would want a competitor's site to get wrong.
Why it matters
Rules differ by destination and change without warning. None of that requires a large budget, only a decision and someone to own it. If two people in the business would answer this differently, that gap is the actual problem.
The steps
- Establish what you have today before changing anything
- Getting it wrong is a compliance problem, not just an accounting one
- Automate it rather than maintaining tables by hand
- Write down the decision so the next person does not re-litigate it
Automate it rather than maintaining tables by hand. This is the sort of thing that compounds, quietly, in both directions. The practical test is whether someone new to the project could tell, in a minute, that it had been handled.
Where to go from here
What this looks like day to day
In e-commerce every friction point has a price attached, and the arithmetic is unusually easy to check. Three things worth confirming about tax calculation before you move on:
- Someone can say what the current setup is without going to look
- Getting it wrong is a compliance problem, not just an accounting one — and you know whether that is true here
- There is a way to tell whether the last change to this helped
None of this needs a rewrite. Most of it is a morning's work once someone decides to do it.