How badly will my credit score be affected if I don't pay back a small margin debt?

Credit scores are not completely transparent, but when I look at my score there's no mention of the magnitude of any events. Truthfully I have no bad events but the only indication is a count (0), not any indication of size.

A bad event is a bad event. It doesn't matter if it's a $10 default or a $10,000 default - it gets reported the same way from what I can tell. It's an indication that you were negligent with the credit that was extended to you.

To clarify based on comments:

There may be some differences in the effect for a small default amount in your score - whether the credit bureau treats it differently, or whether the broker reports it as a default or not, but you can't know that ahead of time, and it is largely irrelevant to my main recommendation:

Scrounge up $50 and pay it off somehow before it turns into a bad mark on your credit that costs way more than $50 down the line.

ANY unpaid debt is negative for your credit. That being said, there are so many different scoring models, even by the same bureau, that it's virtually impossible to assess the consequences. Some might place more emphasis on small unpaid debts relative to larger ones, others may look at installment debt default as more serious than auto debt default or mortgage default.

The bottom line is, find a way to pay the debt QUICKLY! Don't let it linger until it goes to collections and lands on your report. Once there, it'll be difficult to remove even if you pay it, unless the creditor is willing to do so as part of the repayment.

Still, get it paid somehow.

Just open another bank account with a different institution.

Walk in, sit down, leave with a new bank account and routing number. (You may be able to do this online with some institutions, but either way you need to fund the new account with some money you already have.)

Connect it to your brokerage account. Initiate a transfer of money that covers the margin debt.

Like any standardized or aptitude test, the troubles with your existing bank account are a "red herring" and not relevant to the solution.

There is no universal "badness" factor to any delinquent debt reported on a credit report and nobody knows the precise effect it would have on any credit score because there are so many credit scoring models in existence and most of them are proprietary formats that are kept secret from as many people as possible (ie. company insiders only will know the specifics or people with the time/patience to reverse-engineer the models, which has been done in the past but is quickly rendered dated as the models are changed, corrected, updated, improved and generally modified fairly regularly).

The negativity factor of any item reported on your credit is wholly dependent upon how other creditors who use those reports for determining creditworthiness will choose to hold it against you.

Some creditors will look at it and think "Eh, it's a very small amount so he probably just forgot about it or he moved away and doesn't know it's even there. No big deal." while other creditors will look at it and think "Wow, this guy can't even repay $50. And he thinks we're going to approve him for a $1200 computer? Idiot."

Nobody can tell you which experiences you're going to have because nobody knows who will be making future credit decisions based on your credit report. There's a possibility that it doesn't even get reported to any credit bureau (do they generally report your account on a monthly basis? if so, it's almost guaranteed to be reported. if not, it's actually illegal for them to report it on the trade line in many jurisdictions). The trade line is what stays there for the longer period (varies by location, usually about 6 years) but there is a separate section for collection items that it might still get reported in, although these are generally removed after about 3 years.

As others have said, the precise details of credit scores are well-kept secrets, so it's difficult to know the exact effect.

But simply being in debt is not likely to have a negative effect -- that's what loans and margin accounts are for. Your score is impacted if you fail to pay your debts on time.

Furthermore, one late payment should have a minimal impact on your credit score. Everyone messes up occasionally, sometimes a bill gets misplaced. What they look at is your overall history of debt payment.

I'm not sure why you can't just write a check to Ameritrade -- are you concerned that the mail will take too long and you need to get the money to them immediately? Just do your best.

If you still have securities in the account, you can simply sell at least $50 worth, the received funds will go into the margin account automatically.

Pay them by check, credit card, or debit card.

It will damage your credit enough to worry about. How much depends on the rating service, and who you want to use credit with in the future to buy something.

It depends on what you need credit for. It could be that 5 years from now you want something and this $50 debt prevents you from being able to get it. Eventually you will need to pay the debt to get around that problem. Better to deal with it now than down the road.

Dealing with the knock-on effects, not just a ding on your credit, will be WAY MORE hassle than finding a way to pay Ameritrade.

Just call them up and tell them you'd like to pay them and turn off margin trading. Ask how they suggest you do this. If they say to wire the money, just explain that you haven't done it before, it seems complicated, and ask if there's any other way.