You might as well ask, when will household debt be zero? Well, household debt refers to debt owed by a sector of the economy; it is not, you know, an actual person that will retire and move to Florida. Neither will our government retire and move to Florida. Our government is not saving up for the days when it collects no taxes. There is no clicking tock that says it's time for government liabilities to shrink to nothing.
Similarly the corporate sector is never going to "repay" all corporate debt. Corporates are not planning on retiring and earning no more revenue.
Like all other sectors, debt is rolled over and grows with the overall growth of the sector, generally in line with the growth of revenue. For the government, that means tax receipts.
The government is a sector of the economy that will maintain a positive debt level just as households and corporates.
That does not mean that things like interest rate burdens and debt ratios can be ignored. When looking at the health of the corporate sector or the household sector or the foreign sector, we do look at various ratios, and the government sector is no different. But all of these ratios like debt to income for non-financial business assumes that the debt level owed by non-financial business will never be zero.
So asking when government will "pay back" debt is silly. The government will pay back debt when the household, financial, and foreign sector no longer wish to hold liquid risk-free assets and decide to own gold, seashells, and bitcoin instead. That would be never.
My question is more, that given your comment and others suggest it will never been paid completely, why then pay at all? What's the threshold for "we pay this, but not that"?
I think there are plenty of people around here who would be very satisfied if the government of the US did exactly that, as long as it didn't try to claim Medicare.
If the USA wishes maintain the US Dollar's position as the de-facto international currency, then it must maintain a negative balance of trade and high debt levels. Simple fact is that foreigners cannot use USD if they don't have any USD (in the form of cash or US Treasuries). There was once a hope that the Euro could rival the USD but that dream is dead in most people's eyes.
The "private ownership" in that member banks hold stock is also largely symbolic, given that they can't sell the stock and the stock doesn't give them any control, voting rights, etc.
You'd probably see a bidding war over the remaining bills, resulting in slightly negative effective rates. Especially for the 30 year ones, which are currently below 2%.
https://www.ft.com/content/a0482f69-be5c-4d92-ae59-17a8e2b2c...
(This is the modern version of "shortage of specie", shortage of physical coins, which occasionally paralyzed pre modern economies)
https://www.treasury.gov/resource-center/data-chart-center/i...
Not sure if there are also un-adjusted treasuries though. Probably?
Debt isn't inherently bad. However, if mis-managed or abused then both creditors and debtors get into trouble.
Update for clarification - initial response was a bit flippant and not very well considered... Technically phyisical bills ARE debt (they are a liability of the central bank, after all) but they don't _behave_ like debt because they yield 0%.
(The serious answer to the original poster's question is that the US economy is not like a household and the debt does not to be paid off, nor will it ever be paid off.)
There is a real utility to having a vehicle for investing free of credit risk.
You realize how unrealistic that is right?
https://www.ons.gov.uk/economy/nationalaccounts/uksectoracco...
The actual constraints to the issuance of the bonds or money is 1) available natural resources, 2) available labour resources, and 3) inflation (which is usually a result of money issuance or velocity outstripping (1) or (2)).