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What does Claude say?

Most countries around the world have some form of tax reporting requirements, but they vary significantly in who must file returns and under what circumstances. Here's an overview:
Countries where most citizens must file tax returns:

United States
Canada
Australia
Mexico
Brazil
Italy
Spain

Countries with automated systems where many citizens don't need to file:

UK (PAYE system for employees)
Denmark (pre-filled returns)
Sweden (pre-filled returns)
Norway (automated system)
Finland (pre-filled returns)
Estonia (digital pre-filled returns)
Netherlands (pre-filled returns)

Some countries like Japan and Germany have withholding systems where employees below certain income thresholds or with simple tax situations don't need to file. Other countries like Singapore have "no-filing" service programs for eligible taxpayers with straightforward financial situations.
The specific filing requirements depend on factors like:

Income level
Sources of income (employment vs. self-employment)
Residency status
Special deductions or credits being claimed

It's worth noting that even in countries with automated systems, citizens typically need to file returns if they have multiple income sources, investment income, self-employment income, or wish to claim certain deductions.