Same-Day Substitution

Your perfect big sister is getting married. The day of the ceremony, your date gets sick and now you have to go alone. You search around for someone to fill in, someone who will impress your family. But everyone's busy. No one you know has time to go to the wedding. So you end up asking your obnoxious friend...but you make up a fake background and you bribe them to pretend to be someone else for the wedding. There's a whole makeover montage. Hilarity ensues. The plot of Same-Day Substitution...coming to Netflix this fall.

In finance, it has to do with activity in a margin account. Specifically, the term relates to the act of taking money out of your margin account, but then putting in the same amount later that day. So...money goes out, then money comes in...but overall, the balance on the account stays the same.

When you're trading on margin, you need to keep a minium amount in the account. That way, you can cover any margin call that takes place. If you happen to need some cash and taking the amount out puts you below the minimum, you have to replace it, or else you might trigger the margin call for whatever's left in the account.

The quick in/out of the same-day substitution avoids triggering the consequences.