Comment by nubg
8 hours ago
Can somebody explain to me the advantage of double-entry bookkeeping? Is it basically just a "checksum" so it's easier to notice when something is off?
8 hours ago
Can somebody explain to me the advantage of double-entry bookkeeping? Is it basically just a "checksum" so it's easier to notice when something is off?
Double-entry accounting models the source and destination of funds. If you keep all of your money in one bank account and neither owe anyone or have anyone that owes you, then double-entry accounting is not necessary because you can record just the one side of every transaction – your bank account is the other side.
However, if you have more than one account or debts, or budgets, then it becomes useful to track both sides of a transaction. If you track both sides of a transaction then you can easily answer questions like: 1. how much money do I have in my investment account? 2. how much debt do I have? 3. how much did I spend on recreational social activities?
You can track debts and investments separately, but then you are still making two entries just in two places.
I think many people have few enough debts and investment account that they track these separately, and the third question, budgeting, can be simplified if each vendor is only ever considered for a single budget, for example, all your flights are part of your vacation budget, and you don't care to break out a flight to a career related conference.
Yes, it makes it both really simple to spot mistakes and also allows you to easily audit the whole thing after the fact. In corporate contexts it's a straightforward way to make sure your bookies are also honest, just have an external firm look through the whole thing every now and then.
Here is my explanation for "software people who understand databases". The structure of the explanation will be as follows:
1. The way you'd do accounting in a database is with two tables: One table for accounts (e.g. your checking account, or the supermarket account, which you don't own) and another table for transactions. The transactions move an amount of money from one account to another, e.g. from your checking account to the supermarket account. Or if you use it for budgeting, you might split your checking account into a groceries account, a rent account etc. (think "categories").
2. For performance, you would create indices based on the accounts in the transaction table, so you could easily check what's going on e.g. in your groceries account or how much you spent at the supermarket.
3. Double entry accounting was formalized in the 15th century, way before computers became a thing, but bound paper books were already somewhat affordable. The way you'd do accounting is like this: During the business day, you would write down your transactions as they happen, into a scrapbook, similar to the transactions table mentioned above. At the end of the day, you'd do the "double entry" part, which means you take your "index" books where each book is about one account and you transcribe each transaction from your scrap book into the two books of the two accounts that are mentioned in the transaction, e.g. if you spent $10 from your groceries account into the supermarket account, you'd double enter that transaction both into your "groceries" book and into your "supermarket" book. Then, when you want to check on how much you spent at the supermarket in a particular month, you could easily look it up in the supermarket book (this would be very tedious when using the scrap book). These account centered books are like the indices in the database mentioned above.
So the double entry part is about clever index building for making it easier and faster to understand what's going on in your accounting system.
How are investments modeled in this system? e.g I buy $100 of an index fund which can fluctuate in value.
Not an accountant, so if I get it wrong someone please correct me. But index fund shares are an asset: something you own. So is your car, your house (if you own it), and your computer. When you buy an asset, you paid a certain price for it. When you sell it, you pay a different price. Until you sell it, though, you don't actually have the money, so it hardly matters what its value is until you sell it. If you buy $100 of an index fund and a year later it has grown by 10%, you don't actually have $110 yet until you sell it. So you just track that you have a certain number of shares of the fund. Let's say each share sells for exactly $20 when you bought them, so you have exactly 5 shares. Later the share price is $22, but you don't have $110 yet, you still have exactly 5 shares. When you sell them, then you'll have $110.
So you record two entries:
January 1st, 2025:
January 1st, 2026:
At this point you have "realized" ("made real") $10 of profit from this asset. You bought it for $100 and sold it for $110, so the IRS wants you to pay taxes on the $10 profit you made. (This is capital gains tax). Until you sold them, some people would consider you to have $10 profit in "unrealized capital gains", but you did not actually have that profit until you sold the shares. This is important to remember, because if you start counting on that $10 profit but then the share price drops because the economy took a hit, suddenly you don't have $110 worth of shares, you have $90 worth of shares, and you'll make a loss if you sell them now. (This is one of the reasons why only the economically illiterate would propose a tax on "unrealized capital gains": that means taxing people for income they have not actually received, but merely could theoretically receive. Which is both immoral and stupid.)
Hope this explanation helps a little. And as I said, if I got something wrong, please correct me and explain how I was wrong; I'm not an accountant. I understand the basic principles, but it's entirely possible I was off on some detail or other.
3 replies →
Accounts (in the accounting sense) are unitless, and refer to whatever meaning we ascribe to them, so we can transfer value from $ to shares, or USD to GBP or whatever.
Lalit describes this I think really well in his article
https://lalitm.com/post/one-number-i-trust/#chapter-4-invest...
It's not really a checksum. It can sometimes function as one (everything should sum to zero, if it doesn't then you have a math error), but since most records you make will just have two entries (spent $25 on groceries, remove $25 from checking account) the everything-sums-to-zero feature isn't going to catch math mistakes most of the time, because there is no math to be done on most entries. Rather, the fact that everything sums to zero helps you track things later on.
To explain that, I'll rephrase, in my own words, the restaurant example from the article, because that was a good example of the concept. Let's say you went to a restaurant with two friends and decided to split the $90 bill three ways, but your friends didn't have $30 in cash on them at the time. You put the whole $90 on your credit card, and your friends paid you back $30 each the next week: one on Monday, and one on Wednesday.
In single-entry accounting you might have written the following transactions:
Thing is, there's nothing to link those transactions together. If you look at these entries three years later, you'll probably be left scratching your head as to why Alice paid you back $30: there's no $30 transaction, so the $90 restaurant transaction won't jump out at you as the reason why Alice paid you back.
But with double-entry bookkeeping, you'd write that as follows:
Thursday Jan 1st:
Monday Jan 5th:
Wednesday Jan 7th:
It's not always obvious when you're new to double-entry accounting which entries should be positive or negative, but if you remember the "must add to zero" rule you'll be more likely to get it right. Money flowing into an account is positive, money flowing out of an account is negative. For credit cards, the money flows "out of" your credit card and into the restaurant's ownership, so the sign should be negative. When you pay the credit card bill later, the sign will be positive on the credit card account (and negative on your checking account, thus again adding to zero) because money is flowing out of your checking account and into your credit card account.
Now, look at that double-entry accounting. When you look at the Wednesday Jan 5th entry, and you see that Alice paid you back $30, you'll start searching for a $30 transaction earlier, and you'll pretty quickly find the January 1st and figure out that she owed you $30 because you had paid her share of the restaurant bill on the 1st. And even if the amounts don't line up (let's say she paid you $20 on Jan 5th and $10 on Jan 12th), there's still a "money Alice owes me" category which has a +$30 entry on the 1st, then -$20 on the 5th and -$10 on the 12th, all of which makes it pretty easy to figure out what Alice is paying you back for.
So by recording each entry in at least two places (it's not always exactly two places, e.g. the January 1st expense is recorded in four places total), you get more linkage between the items and it becomes a lot easier to see why the money was going out or coming in.
I must have read half a dozen intro-to-accounting books, and it never ever clicked for me. I understood the concepts, the benefits, but it just felt 'wrong'.
It wasn't wrong of course, there is so much history, ingenuity and the invention of double entry accounting, but I just couldn't get my brain to understand it.
The way the concepts settled in my head was: double entry accounting is just an excellent way of modelling a graph with nodes and edges. Accounts are nodes, transfers are edges. Every edge has a source and a destination.
For a paper ledger, each column is graph node, and each row is a graph edge.
That was enough for me to be able to learn the rest of the things I needed for interacting with the accounting world.
But I also realised that that description really only helps a very small part of the population. :D It makes things so much worse for most people.
"Hey could you help me understanding this accounting thing?"
"Sure, but first thing is, let's learn graph theory! You know who Dijkstra right?"
Whole buckets of nope.
But thats a digression from your actual question - whats the point?
It presents a rigid set of rules of recording transfers, everything has to have a from account and to account (i.e. a graph edge), every row must add up to zero.
Because of that, it makes it easy to spot any mistakes in data entry. If any of your rows dont add up to zero - then you've made a mistake.