When tax calculation is worth the effort

The version of this that works is simpler than the version most people imagine. Tax calculation is not free, and pretending otherwise leads to bad decisions.

Small percentage changes matter here because they apply to every order, every month. Doing this properly once is usually cheaper than doing it approximately three times.

When it is worth it

Rules differ by destination and change without warning. None of that requires a large budget, only a decision and someone to own it. The version that survives contact with a real deadline is the simple one.

When it is not

If nothing downstream depends on it and nobody is complaining, it can wait. This is the sort of thing that compounds, quietly, in both directions.

How to decide

Automate it rather than maintaining tables by hand. The teams that handle this well are rarely the ones with the biggest budgets. Doing this properly once is usually cheaper than doing it approximately three times.

In practice

Trust does most of the selling online, and trust is built from unglamorous details. Three things worth confirming about tax calculation before you move on:

• Someone can say what the current setup is without going to look
• Rules differ by destination and change without warning — 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.