# When should I calculate tax?

Source: https://developer.avalara.com/avatax-for-vat/ntp2066835740015/

# When should I calculate tax?

Learn when to calculate tax in your system to balance API efficiency and transaction workflow needs.

Getting a tax calculation is the primary reason developers use AvaTax, and [CreateTransaction](https://developer.avalara.com/api-reference/avatax/rest/v2/methods/Transactions/CreateTransaction/) is the starting point.

But when will you collect tax? The answer varies from system to system, but in general, it depends on the balance between efficient API usage and your application's transaction workflow requirements.

If you are using the VAT Ecommerce solution, you'll want to show tax in the checkout workflow, which is after the user has entered their shipping and billing information.

Note

Be sure that your system isn’t calling tax every time a line is added or changed because this can drive up usage.

Tip

Consider providing an explicit **Calculate tax** button, or simply calculate tax automatically before saving the document.