BUCH, Judge: Eric Stephen Gerencser is a U.S. citizen who lived and worked in Germany as a North Atlantic Treaty Organization (NATO) contractor during 2010 and 2011, the years in issue. For his NATO wages, Mr. Gerencser claimed both a section 911 foreign earned income exclusion and a foreign tax *152 credit.¹ The Commissioner allowed the foreign earned income exclusion but disallowed the foreign tax credit because it would be an impermissible double benefit to exclude income and then claim a credit with respect to that same income.² As to other non-NATO income, Mr. Gerencser argues that he is entitled to a foreign tax credit, but his argument fails because he has not shown that he has paid or accrued any foreign taxes with respect to that income.³ He also argues that the Convention between the United States of America and the Federal Republic of Germany for the Avoidance of Double Taxation and the Prevention of Fiscal Evasion With Respect to Taxes on Income and Capital and to Certain Other Taxes,⁴ as amended by the 2006 Protocol⁵ (Treaty), provide him relief because he qualifies as a German2016 Tax Ct. Memo LEXIS 149">*150 resident. The Treaty's saving clause reserves the right of *153 the United States to tax its citizens on their worldwide income, regardless of their residence. Because Mr. Gerencser is a U.S. citizen, he is not entitled to treaty relief. Further, he is liable for the section 6662(a) accuracy-related penalty because he negligently took an impermissible double benefit when he claimed both foreign earned income exclusions and foreign tax credits on his NATO wages.

Mr. Gerencser, a U.S. citizen, worked as a NATO contractor in Heidelberg, Germany, during 2010 and 2011. The parties stipulated that he was subject to the Protocol2016 Tax Ct. Memo LEXIS 149">*151 on the Status of International Military Headquarters Set Up Pursuant to the North Atlantic Treaty.⁶ Under article 7, paragraph 2 of this agreement, amounts paid for service as personnel of an Allied Headquarters are exempt from German tax.

To obtain an explanation of his tax situation, Mr. Gerencser wrote a letter dated May 6, 2009, to the Commissioner; he did not receive a response. After speaking with a colleague, Mr. Gerencser came to the understanding that he could owe a retroactive German income tax once his contract with NATO expired *154 because Germany would retroactively treat him as a German resident who was subject to German tax.

Mr. Gerencser filed Forms 1040, U.S. Individual Income Tax Return, for 2010 and 2011. For 2010 he reported $120,530 in NATO wages and claimed a foreign earned income and housing exclusion of $120,460 and a foreign tax credit of $26,716. He also reported U.S. military pension income, taxable interest, dividends, rental income, and a capital loss from securities transactions for that year. Similarly, for 2011 he reported $119,673 in2016 Tax Ct. Memo LEXIS 149">*152 NATO wages and claimed a foreign earned income and housing exclusion of $117,436 and a foreign tax credit of $35,229. In addition, he reported U.S. military pension income, taxable interest, dividends, rental income, and a capital gain from securities transactions.

On November 15, 2013, the Commissioner issued to Mr. Gerencser a notice of deficiency for taxable years 2010 and 2011. The Commissioner determined the following deficiencies in tax and accuracy-related penalties:

Among other adjustments, the Commissioner determined that Mr. Gerencser was not entitled to a foreign tax credit on his NATO wages because he had claimed *155 those wages were exempt under the foreign earned income exclusion. The Commissioner also determined that Mr. Gerencser had an additional capital gain for 2010 of $15,351 and was not entitled to $1,460 in itemized deductions for 2010.

When Mr. Gerencser received this notice of deficiency, he had a case pending before our Court involving his 2009 taxable year.⁷ On February 20, 2014, the Court entered a stipulated decision pursuant to an agreement of the parties that Mr. Gerencser did not owe any additional2016 Tax Ct. Memo LEXIS 149">*153 tax or penalties for 2009.

Mr. Gerencser timely filed his petition while residing in Germany, and trial was held in Las Vegas, Nevada. The parties have agreed that he is not liable for tax on the unreported capital gain for 2010 and that he is entitled to the disallowed itemized deductions for 2010. The parties further stipulated that he "is not entitled to claim a foreign tax credit with respect [to] his wages from NATO for taxable years 2010 and 2011." Mr. Gerencser has not paid any German income taxes for the 2010 or 2011 taxable year as to either his NATO or his non-NATO income.

We must decide whether Mr. Gerencser is entitled to foreign tax credits or treaty benefits related to his non-NATO income. To do so, we apply the foreign tax credit rules under the Code and the Treaty.

The Commissioner's determinations in the notice of deficiency are generally presumed correct, and taxpayers bear the burden of proving otherwise.⁸ Allowing foreign tax credits is an act of legislative grace, and taxpayers must prove that they have met all the conditions to be entitled to any credit.⁹ In limited situations the burden may shift to the Commissioner under2016 Tax Ct. Memo LEXIS 149">*154 section 7491(a), but there is insufficient information in the record to conclude that the burden should shift under section 7491(a), and Mr. Gerencser does not argue that the burden should shift. Accordingly, the burden remains on him.

Section 901 allows taxpayers a foreign tax credit for foreign income, war profits, and excess profits taxes they have paid or accrued during the taxable *157 year.¹⁰ Taxpayers, including cash basis taxpayers, may elect to take foreign tax credits for the year the taxes accrued.¹¹ However, no credit is allowed for accrued taxes that are not paid within two years after the close of the taxable year to which they relate.¹² If taxpayers subsequently pay foreign taxes,¹³ then they can file a claim for a credit or refund within 10 years from the date prescribed by law for filing the return for the year for which such taxes were actually paid.¹⁴

Section 911(a) allows qualified individuals, as defined in subsection (d), to exclude from their gross income a portion of their foreign earned income and housing costs.¹⁵ For any amount of foreign earned income2016 Tax Ct. Memo LEXIS 149">*155 that is excluded under section 911(a), taxpayers cannot take a double benefit by claiming tax credits on *158 the same income.¹⁶ If taxpayers elect the foreign earned income and housing exclusion treatment for their foreign earned income, they likewise cannot take a foreign tax credit for any tax paid on the foreign earned income that was excluded.¹⁷

Mr. Gerencser is not entitled to a foreign tax credit on his NATO wages for the years in issue because he has already excluded them from income using the foreign earned income and housing cost exclusion of section 911(a). For 2010 the Commissioner allowed Mr. Gerencser to exclude $120,460 total, which includes $28,960 of housing costs and $91,500 of foreign earned income. For 2011 the Commissioner allowed Mr. Gerencser to exclude $117,436 total, which includes $24,536 of housing costs and2016 Tax Ct. Memo LEXIS 149">*156 $92,900 of foreign earned income. And even if Mr. Gerencser had paid or accrued foreign tax on these wages, which he has not, he would not be entitled to a foreign tax credit because it would violate the *159 impermissible double benefit rule of section 911(d)(6). The parties further agreed that he is not entitled to a foreign tax credit for his NATO wages.

Mr. Gerencser is not entitled to a foreign tax credit relating to his non-NATO income because he has not paid any foreign tax. For 2010 and 2011 he reported U.S. military pension income, taxable interest, dividends, rental income, and capital losses from securities transactions, but he has not paid any German income taxes for 2010 or 2011. Even if Mr. Gerencser had elected a credit for accrued foreign tax credits, he cannot receive the benefit of accrued foreign taxes because he did not pay any taxes within two years after the close of the 2010 or 2011 tax year.¹⁸ Accordingly, he is not entitled to any foreign tax credits on his other income streams at this time.

Mr. Gerencser argues that because he is a resident of Germany,2016 Tax Ct. Memo LEXIS 149">*157 his income should be exempt from U.S. tax under the Treaty.¹⁹ He is wrong. The United *160 States reserves the right to tax its citizens on their worldwide income, regardless of their residence,^{202016 Tax Ct. Memo LEXIS 149">*158} and Mr. Gerencser is a U.S. citizen. The Treaty reflects this approach in the saving clause: "Except to the extent provided in paragraph 5, this Convention shall not affect the taxation by the United States of its residents (as determined by Article 4 (Residence)) and its citizens."²¹ We have previously explained that the "United States insists on the inclusion of a 'savings clause' in its tax treaties; the effect of this clause is to reserve the right of the United States to tax its citizens and residents on the basis of the provisions of the Internal Revenue Code without regard to the provisions of the treaty."²² None of *161 the income that Mr. Gerencser had during the years in issue is exempt from the saving clause.²³

Although the saving clause does not affect the treaty rules for relief from double taxation found in article 23, this article provides that the United States will allow a credit for income taxes paid to Germany.²⁴ But Mr. Gerencser has not paid any income taxes to Germany.

Mr. Gerencser further argues that the Treaty and the Code are in conflict and that he should be entitled to treaty relief despite not filing treaty-based returns for the years in issue. It is well established that neither2016 Tax Ct. Memo LEXIS 149">*159 a treaty nor a law takes precedence merely by virtue of its status as a treaty or law.²⁵ If there is a conflict between a Code provision and a treaty provision, then the provision that was enacted later in time controls.²⁶ But there first must be an irreconcilable conflict, because "when a treaty and a statute relate to the same subject, courts will always *162 attempt to construe them so as to give effect to both".²⁷ Mr. Gerencser's conflict arguments fail because the saving clause of the Treaty bars him from obtaining relief. There is no conflict between the Code and the Treaty.

Section 6662(a) and (b)(1) and (2) imposes a 20% accuracy-related penalty on any portion of an underpayment of tax required to be shown on a return if the underpayment is due to, among other reasons, negligence, disregard of rules or regulations, or any substantial understatement of income tax. The Commissioner bears the burden of production as to penalties.²⁸ Penalties will not apply to any portion of the underpayment for which a taxpayer establishes that he or she had reasonable cause and acted in good faith.²⁹

As defined in2016 Tax Ct. Memo LEXIS 149">*160 the Code, negligence includes any failure to make a reasonable attempt to comply with the provisions of title 26, and the term *163 "disregard" includes any careless, reckless, or intentional disregard.³⁰ Negligence has been further defined as a "lack of due care or failure to do what a reasonable and ordinarily prudent person would do under the circumstances."³¹ Additionally, a taxpayer is negligent if he fails to maintain sufficient records to substantiate the items in question.³²

The Commissioner satisfied his burden of production because he showed that Mr. Gerencser negligently took foreign tax credits for his NATO wages that he had also claimed were excluded from his gross income by the foreign earned income and housing cost exclusion; a double benefit that is directly and expressly prohibited by the Code.

If a taxpayer takes a return position that would seem "too good to be true" to a reasonable person and fails to make further reasonable inquiries to verify that the return position is correct, then this is a strong indication that the taxpayer is *164 negligent.^{332016 Tax Ct. Memo LEXIS 149">*162} Taxpayers are "required to take reasonable steps to determine the law and2016 Tax Ct. Memo LEXIS 149">*161 to comply with it"³⁴ and must exercise due care when claiming a deduction.³⁵ Here, a reasonable person would have thought the double benefit of a foreign tax credit and a foreign earned income exclusion on the same income seemed too good to be true, and Mr. Gerencser had a duty to inquire further before taking this position. After hearing about his colleague's predicament, Mr. Gerencser sent a letter to the Commissioner to further inquire but never received a response. Instead of seeking out competent advice from a tax professional, he prepared his returns and explained that he "had to come up with my own way to file those taxes that would cover, so to speak, the waterfront and capture my *165 situation." Because he did not make a reasonable inquiry to determine whether his return position was correct, he was negligent.

Mr. Gerencser did not prove he acted with reasonable cause and in good faith. Although Mr. Gerencser wrote to the Commissioner to ask for guidance, he never received a response. Instead, he believed that he would be taxed at some time in the future by Germany because of the conversations he had with his colleague, who was not a tax professional. He then reported both the foreign income and housing cost exclusion and foreign tax credit for his NATO wages. His position is not reasonable because it would provide him a double benefit. Further, Mr. Gerencser did not show that he had paid or accrued any foreign taxes to entitle him to offset his U.S. tax with foreign tax credits.

Mr. Gerencser appears to argue that the stipulated decision entered in 2014 for his 2009 taxable year should affect the outcome of this proceeding or at least should prove that his position was reasonable. To the extent that he is making a collateral estoppel argument, this argument fails because the previous stipulated decision entered for 2009 was not a2016 Tax Ct. Memo LEXIS 149">*163 conclusive determination on the merits by our Court.³⁶ Moreover, we look at whether the position taken by Mr. Gerencser on his *166 return was negligent. Mr. Gerencser filed his returns for 2010 and 2011 before he commenced his 2009 case and years before he entered into a stipulated decision.

Mr. Gerencser's underpayment of tax was due to his negligence, and he is liable for the section 6662(a) accuracy-related penalties for both years.

Mr. Gerencser is not entitled to any foreign tax credits because he has not paid2016 Tax Ct. Memo LEXIS 149">*164 or accrued any foreign tax. Accordingly, we sustain the Commissioner's disallowance of the foreign tax credits Mr. Gerencser claimed for 2010 and 2011 and find him liable for the section 6662(a) accuracy-related penalties for those years.

*167 To reflect the foregoing,

Decision will be entered under Rule 155.