There is a general pattern for the stages of hyperinflation. This can also be viewed as the stages of the "death of a fiat currency". Money can be seen as serving 3 roles. It is a medium of exchange, it is a store of value, and it is a unit of accounting. As we move through the stages of hyperinflation the money gradually gives up these 3 roles. Once it has given up all 3, it is dead.
- Government spending gets out of control to where deficit is 40% or more of spending and debt is over 80% of GNP. If this is for a war that the markets believe will be won and ended so that the government can make drastic cuts in spending, then there is some wiggle room in these numbers.
- This goes on for a couple years and investors move towards shorter-term bonds.
- It becomes clear the deficit is not going back down.
- The central bank starts buying up government debt with newly made money. If they are not naturally inclined to do this, the government changes the laws or people running the central bank. For the rest of this section, I will write as if the central bank were just part of the government and ignore bond certificates printed by the government and handed to the central bank as these will become worthless anyway. With this simplification, I will just say, "the government prints money".
- There is capital flight out of that currency and bond sales fail. If the government let bond interest rates rise to attract bond buyers, the interest payments on the debt would be huge compared to taxes collected, so they keep interest rates down by printing more money. However, the private investors become less and less inclined to "roll over" their government bonds.
- Government is forced to print money to cover their budget and inflation picks up. The more bonds coming due the worse the printing is. Many short-term bonds can make for huge amounts of printing, even more than the regular budget.
- Some people notice prices going up and spend their money before prices go up more, even for things they don't need yet. The velocity of money picks up. People start to realize that the local currency is not a good store of value, though still used for transactions. Some people start to use foreign currencies or gold as a store of value.
- So many people take money out of their bank accounts and exchange it for a foreign currency, or gold, or just buy something, which puts banks in danger of going under. So the government often freezes bank accounts. This is very bad for the account holders, both because times are hard and they can't get their money, and also because by the time they are able to get their money, it is worth much less.
- Wages and prices become indexed to something more stable, like a foreign currency or gold. So the local currency is losing the "unit of account" function. Wages become paid more often, like weekly or daily, instead of monthly. The velocity of money picks up more.
- People start to use a foreign currency or gold as store of value, even though the government may forbid it. The black market starts in currency exchange.
- Interest rates are very high and loans are for much shorter periods. Loans may be for a couple months instead of 30 years. Hyperinflation makes for hard times and many people are forced to sell their their land or house. Because of these things the real prices for things usually bought with long-term loans can drop in terms of something like gold. Houses may usually be bought with a bag of some foreign currency. Real estate is very different during hyperinflation and normal times.
- People start to use barter or a foreign currency or gold for trade, even though the government forbids it. This is a growing black market for commerce. If you trade a fish you caught for some potatoes your friend grew, neither of you is paying any taxes on the deal. In general, once people are breaking the law by using a foreign currency for trade, they don't pay any taxes on trade either. The black market is tax free.
- Being tax free and with better store of value, the black market eventually grows larger than the legal market. People no longer worry about the government requirement to use local paper currency, enforcement is impossible.
- A business that follows the law and sells for regulated prices in the local currency cannot buy enough new inventory and soon goes out of business. This makes the percentage of the economy that is black market go up.
- People start to not want to accept the local paper money. Regular taxes are down because hyperinflation has devastated the economy and much of the economy is now in the "black market". The government is finding it hard to buy things by printing money, as so much of the economy has moved to the black market. It is finding it hard to pay employees enough for them to live comfortably, even though it keeps printing more all the time. The government is losing economic power. Tax collectors may be skipping work to tend to their own vegetable garden. There is a very real risk of the government failing at this step.
- At this point, the government has some hard choices if it is not going to fail. It needs to do something so that the "black market" is legalized and taxable, and deficits are nearly eliminated. It could just legalize a foreign currency or gold. But then it would forever give up on collecting any "inflation tax". It could get rid of budget deficits and stop printing money. However, people will still fear that it could start again at any time and so be hesitant to use that money. I think the most frequent end to hyperinflation is by making a new fiat money but with enough governmental changes that bring deficits and inflation under control, people will use the new money. If they switch to a new currency then the old money is no longer used as a store of value, or unit of account, or even as a medium of exchange. It has died.
For more details on the stages of hyperinflation, and historical examples, I highly recommend Monetary regimes and inflation: history, economic and political relationships by Peter Bernholz.