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Stock and flow

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I’ve already made it very

clear what I think about credit cards: this post is an attempt to flesh

out one theory of how and why they work the way they do – to the benefit

of banks and the detriment of consumers. On the one hand it’s all blindingly

obvious, but on the other it’s not something I’ve really seen spelled out in

quite this way, so I thought I’d take a crack at it.

Most people, if you ask them what their highest-value asset is, might point

to their car, or their heavily-mortgaged house, or something like that. In fact,

their highest-value asset is much more likely to be their job: the present value

of their future income is enormous, and almost certainly worth more than their

home even without a mortgage. But although people don’t really think that way,

they do understand it on a gut level, just as they understand asset-liability

mismatches on a gut level.

What I’m talking about here is the difference between stock and flow, and the

way in which credit card companies take advantage of that difference to make

enormous profits. In financial markets, of course, there’s always someone willing

to convert stock to flow or flow to stock: any given income stream is worth,

today, a certain fixed amount of money. If I have a stock of money, I can convert

it into an income stream by buying bonds, and if I have an income stream there’s

bound to be someone I can sell it to for a fixed amount.

When it comes to personal finance, however, the equivalence breaks down. You

can’t monetize the present value of your future income: I can’t go to some broker

and tell him he can have 10% of all my future earnings in return for an upfront

payment of, say, twice my annual income.

As a result, unable to switch at will between stock and flow, people like to

match their assets to their liabilities. If their main asset is a flow –

their income – then their liabilities should be flow liabilities too.

Why did so many people feel uncomfortable about privatization? Because it took

a stock asset (a national company), sold it, and then applied the proceeds to

flow liabilities – the general fiscal account. It was called "selling

off the family silver" to pay day-to-day expenses: an asset-liability mismatch.

The general idea is that flow liabilities – the monthly bills –

should only be paid with flow assets – monthly income. Selling off assets

to pay the bills is unsustainable.

The genius of credit cards is that they slowly and invidiously turn flow liabilities

into stock liabilities. A credit card is a wonderful way of paying for something

today if you’re not going to get paid until tomorrow. So long as you pay off

your debt at the end of the month, it’s an interest-free loan: free money. It

feels like flow debt rather than stock debt: you use your income over the course

of the month to pay for your purchases over the course of the month.

Credit-card debts increase in small increments: a purchase here, a purchase

there, a finance charge at the bottom of the statement. Any individual purchase

can be justified. Here’s a thought experiment: tell someone that he has a credit

card with a $5,000 credit limit, and let him make purchases until the credit

limit is reached. There’s a good chance he’ll do so, even if the interest rate

on the card is over 20%. Now, take that same person, and offer him a $5,000

loan, unsecured, at an interest rate of 10%, which he can then spend on whatever

he likes. There’s a good chance he’ll refuse, even though going that route would

save him money in the long term compared to going down the credit-card route.

That’s because the second choice is stock debt, and people don’t like stock

debt because they don’t have stock assets. The first choice is flow debt, and

that’s fine, because people do have flow assets – their income.

What’s more, people always underestimate their future expenditures. They’ll

buy something now, justifying it with the idea that they’ll spend less next

month – something they rarely do. Most people who max out their credit

cards don’t intend to max out their credit cards. It just happens, almost while

they’re not watching. That’s another reason why our thought-experiment guy will

refuse the $5,000 loan: even if he understands that it would work out cheaper

than a $5,000 credit-card balance, he doesn’t think he’d ever max out a $5,000

credit card. A loan carries debt service whether it’s spent or not, so in fact

it’s rational to take the credit card rather than the loan if you think you

won’t carry much of a balance on it.

But anyone who’s ever got a credit card bill, whether they’ve paid it off in

full or not, has suffered a certain amount of cognitive disconnect between the

large number at the bottom of the bill and the seemingly small numbers which

constitute it. How could a series of individually small transactions add up

to such a huge amount? When you’re out there spending, it really doesn’t seem

that big. But when the bill arrives, suddenly those flow transactions –

day-to-day monthly expenses – have been transmogrified into a whopping

great big stock of debt.

That’s why, individuals would be much better off if they took out loans to

pay their expenses than if they borrowed on their credit cards. (They’d be better

off still living within their means, of course.) But loans are large, up-front,

stock transactions. They can be justified in exceptional cases, such as buying

a house or a car, or starting up a business. But people won’t take out a loan

to pay a restaurant bill, because they’ll be paying off the loan long after

the asset they’ve bought with it has been literally flushed down the toilet.

What’s more, any fool can see that if you need to take out a loan to pay a

restaurant bill, you shouldn’t be eating at that restaurant. Increasing your

stock of debt for the sake of a flow transaction like eating out is a classic

asset-liability mismatch. And yet people pay for their meals on their credit

cards the whole time, and, as often as not, fail to pay those credit cards off

in full every month. To all intents and purposes, they’ve borrowed the money

for the meal, and they’re paying interest on it at exorbitant rates.

Credit cards, then, are a wonderful way for banks to help consumers delude

themselves that they’re living within their means. Most people who carry a revolving

balance on their credit cards are simply spending more than they’re earning,

month in and month out. It’s unsustainable, but the existence of their credit

cards lets them get away with it for a much longer time than if they had to

justify their expenditures to their bank manager. The key hurdle becomes not

"can I pay my entire bill off in full at the end of each month", but

rather "can I pay the minimum amount at the end of each month". The

answer to the second question is nearly always yes – until you’re in a

hole of enormous magnitude.

Eventually, this entire edifice of credit-card debt could come crashing down

onto the banks, causing them as much harm as it’s presently causing consumers.

For the time being, however, they’re making billions from it. If that annoys

you, you can do your bit. Pay off all your credit cards with a loan –

one secured on your home, if necessary – and always pay them off in full

every month from here on in. Otherwise you’re just pissing your money away.


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