Honest question, how much of that is being spent on NATO commitments and participating in the defence of Europe ?
Difficult to answer, however the question has been asked and discussed elsewhere. An excerpt from a 2018 piece.
www.csis.org
. . .
Guesstimating the Real Cost to the U.S. of Its Forces for NATO
Unfortunately, there is no official U.S. or NATO source that does estimate the actual portion of total U.S. defense spending that should be allocated to NATO. Such U.S. estimates were made in the past as a result of legislative action in the Senate Armed Services Committee by Senator Nunn and Senator Warner. The requirement for such reporting has long since lapsed, however, and there are no official U.S. estimates of what the U.S. currently actually spends on NATO.
Outside guesstimates of the costs of deploying U.S. forces outside the U.S. have uncertain credibility, but their size does show that they are only likely to be a fraction of 70%. For example, one recent low-end estimate puts the incremental cost of
every U.S. overseas base and deployment at roughly $150 billion a year. This total would be only 24% of the low $706.1 billion total that
Figure A1 shows NATO reports for total U.S. defense spending in current dollars in 2018, and only 16% of the total of $706.1 billion it reports for all of NATO. And once again, it should be stressed that this guesstimate of the burden, however, includes all U.S. forces in Asia, the Middle East, Africa, and in the rest of the world.
An admittedly rough estimate by the International Institute of Strategic Studies (IISS) has far more credibility.
[1] It only attempts to estimate the cost of U.S. forces in Europe and
estimates that, "direct US expenses on defense in Europe (in current dollars) are estimated to range between US $30.7bn in 2017 and US $36.0bn in 2018, or between 5.1% and 5.5% of the total US defense budget, as measured by the IISS ($602.78 billion). These numbers, it could be argued, put the total defense spending of European NATO allies – US $239.1bn – in something of a different light." The $36.0 billion figure for 2018 would be only 5.1% of the $706.1 billion total reported by NATO – making the 70% some 64.9% higher.
As the IISS points out,
however, simply costing the U.S. forces in Europe does not include the cost of any forces in the U.S. that are effectively dedicated – or earmarked or assigned to reinforcing NATO in a credible emergency or warfighting case. If one somewhat arbitrarily
assumes that the total cost would be some three times higher than the cost of U.S. forces actually in Europe, a round number of $100 billion might be as good a guess as any. This would still, however, be a maximum of 14.1% of the U.S. total of $706.1 billion in current dollars that NATO reports for the U.S. in 2018. It would also be only 25% of the revised $ 407.3 billion total cost for NATO in 2018 – which would include $285.7 billion for NATO Europe and $21.6 billion for Canada.
So, possibly between 5% and 15% of the US defence budget. Of course, it could be much higher if troops were directly involved in a shooting war.
