You can browse the US Code on the House of Representatives&#x27; website.<p>Here&#x27;s 26 USC Subtitle F, &quot;Procedure and Administration&quot;:<p><a href="http:&#x2F;&#x2F;uscode.house.gov&#x2F;view.xhtml?path=&#x2F;prelim@title26&#x2F;subtitleF&amp;edition=prelim" rel="nofollow">http:&#x2F;&#x2F;uscode.house.gov&#x2F;view.xhtml?path=&#x2F;prelim@title26&#x2F;subt...</a><p>Duty to file an income tax return is section 6012 on that page. Section 6151 lays out the duty to pay tax and when the tax must be paid (at time of filing).<p>You&#x27;ll also notice if you play around with it that the House site is pretty terrible to browse and read, which is why everybody links to Cornell&#x27;s version.