Mortgage-backed securities I | Finance & Capital Markets | Khan Academy

Welcome to my presentation on mortgage-backed securities.

Let's get started.

And this is going to be part of a whole new series of

presentations, because I think what's happening right now in

the credit markets is pretty significant from, I guess, a

personal finance point of view and just from a

historic point of view.

And I want to do a whole set of videos just so people

understand, I guess, how everything fits together, and

what the possible repercussions could be.

But we have to start with the basics.

So what is a mortgage-backed security?

You've probably read a lot about these.

So historically, let's think about what historically

happens when I went to get a loan for a house, let's say,

20 years ago.

And I'm going to simplify some things.

And later we can do a more nuanced.

Where'd my pen go?

Let's say I need $100,000.

No, let me say $1 million, because that's actually closer

to how much houses cost now.

Let's say I need a $1 million loan to buy a house, right?

This is going to be a mortgage that's going to be

backed by my house.

And when I say backed by my house, or secured by my house,

that means that I'm going to borrow $1 million from a bank,

and if I can't pay back the loan, then the

bank gets my house.

That's all it means.

And oftentimes it'll only be secured by the house, which

means that I could just give them back the keys.

They get the house and I have no other responsibility, but

of course my credit gets messed up.

But I need a $1 million loan.

The traditional way I got a $1 million loan is I would go and

talk to the bank.

This is the bank.

They have the money.

And then they would give me $1 million and I would pay them

some type of interest. I'll make up a number.

The interest rates obviously change, and we'll do future

presentations on what causes the interest rates to change.

But let's say I would pay them 10% interest. And for the sake

of simplicity, I'm going to assume that the loans in this

presentation are interest-only loans.

In a traditional mortgage, you actually, your payment has

some part interest and some part principal.

Principal is actually when you're paying down the loan.

The math is a little bit more difficult with that, so what

we're going to do in this case is assume that I only pay the

interest portion, and at the end of the loan I pay the

whole loan amount.

So let's say that this is a 10-year loan.

So for each year of the 10 years, I'm going to pay

$100,000 in interest. $100,000 per year, right?

And then in year 10, I'm going to pay the $100,000 and I'm

also going to pay back the $1 million.


Year 1, 2, 3, dot, dot, dot, dot, 9, 10.

So in year one, I pay $100,000.

Year two, I pay $100,000.

Year three, I pay $100,000.

Dot, dot, dot, dot.

Year nine, I pay $100,000.

And then year 10, I pay the $100,000 plus I pay back the

$1 million.

So I pay back $1.1 million.

So that's kind of how the cash is going to be transferred

between me and the bank.

And this is how a-- I don't want to say a traditional

loan, because this isn't a traditional loan, an

interest-only loan-- but for the sake of this presentation,

how it's different than a mortgage-backed security, the

important thing to realize is that the bank would

have kept the loan.

These payments I would have been making would have been

directly to the bank.

And that's what the business that,

historically, banks were in.

Another person, you-- and you have a hat-- let's say you're

extremely wealthy and you would put $1

million into the bank.


That's just your life savings or you inherited

it from your uncle.

And the bank would pay you, I don't know, 5%.

And then take that $1 million, give it to me, and get 10% on

what I just borrowed.

And then the bank makes the difference, right?

It's paying you 5% percent and then it's getting 10% from me.

And we can go later into how they can pull this off, like

what happens when you have to withdraw the money,

et cetera, et cetera.

But the important thing to realize is that these payments

I make are to the bank.

That's how loans worked before the mortgage-backed security

industry really got developed.

Now let's do the example with a mortgage-backed security.

Now there's still me.

I still exist. And I still need $1 million.

Let's say I still go to the bank.

Let's say I go to the bank.

The bank is still there.

And like before, the bank gives me $1 million.

And then I give the bank 10% per year.


So it looks very similar to our old model.

But in the old model, the bank would keep

these payments itself.

And that $1 million it had is now used to pay for my house.

Then there was an innovation.

Instead of having to get more deposits in order to keep

giving out loans, the bank said, well, why don't I sell

these loans to a third party and let them do

something with it?

And I know that that might be a little confusing.

How do you sell a loan?

Well let's say there's me.

And let's say there's a thousand of me.


There's a bunch of Sals in the world.


And we each are borrowing money from the bank.

So there's a thousand of me.


I'm just saying any kind of large number.

It doesn't have to be a thousand.

And collectively we have borrowed a

thousand times a million.

So we've collectively borrowed $1 billion from the bank.

And we are collectively paying 10% on that, right?

Because each of us are going to pay 10% per year, so we're

each going to pay 10% on that $1 billion.


So 10% on that $1 billion is $100 million in interest. So

this 10% equals $100 million.

Now the bank says, OK, all the $1 billion that I had in my

vaults, or whatever-- I guess now there's no physical money,

but in my databases-- is now out in people's pockets.

I want to get more money.

So what the bank does is it takes all these loans

together, that $1 billion in loans, and it says, hey,

investment bank-- so that's another bank-- why don't you

give me $1 billion?

So the investment bank gives them $1 billion.

And then instead of me and the other thousands of me paying

the money to this bank, we're now paying it to this new

party, right?

I'm making my picture very confusing.

So what just happened?

When this bank sold the loans-- grouped all of the

loans together and it folded it into a big, kind of did it

on a wholesale basis-- it's sold a thousand

loans to this bank.

So this bank paid $1 billion for the right to get the

interest and principal payment on those loans.

So all that happened is, this guy got the cash and then this

bank will now get the set of payments.

So you might wonder, why did this bank do it?

Well I kind of glazed over the details, but he probably got a

lot of fees for doing this, or maybe he just likes giving

loans to his customers, whatever.

But the actual right answer is that he got

fees for doing this.

And he's actually probably going to transfer a little bit

less value to this guy.

Now, hopefully you understand the notion of actually

transferring the loan.

This guy pays money and now the payments are essentially

going to be funnelled to him.

I only have two minutes left in this presentation, so in

the next presentation I'm going to focus on what this

guy can now do with the loan to turn it into a

mortgage-backed security.

And this guy's an investment bank instead of

a commercial bank.

That detail is not that important in understanding

what a mortgage-backed security is, but that will

have to wait until the next presentation.

See you soon.