Take a look at that vin foundation calculator and plug in loan amounts to get a better idea.
I'm making up numbers here, but let's say you owe $250k at the time you go into repayment. Just interest alone is $1500 per month on that loan. Let's say you only need to pay $500 per month on PAYE. That means your loans are ballooning at the rate of $1000 per month. Over 20 years (240 months), your loan grows to $490k.
That whole amount is forgiven yay! But let's
Say you are earning 100k that year. Your income therefore for that year is $590k! Awesome you're like a 1%er that year
so you get to be taxed as someone earning $590k, so likely the highest tax bracket which if it were this year is around 40%. Add state income tax on top of that, and you probably owe somewhere between 40-47% of the forgiven $490k in taxes, which had not been deducted throughout the years automatically like your regular income. So you owe the Feds anywhere from $200-250k in taxes. The idea is that you owe it all at once when you file your taxes that year. You are supposed to have saved for this (so essentially you should have been putting away $1000/month into a savings account or investment account).
Again, you can look at the vin foundation calculator and it will tell you how much you will likely owe in taxes at the end, depending on your situation.
No one's been forgiven yet. Given Americans' general lack of ability to plan, in 10-15 years or so when the first people get forgiveness, this is likely going to result in some sort of crisis because people won't be able to pay that tax. Who knows how the government will deal with that.