How to correctly calculate take-rate

Recently I had to calculate the take-rate metric for a classifieds project, and I noticed that for projects like this it tends to be calculated not quite correctly, so I decided to share my thoughts on the matter.

Let's start with what take-rate is in classifieds — it's a metric that shows how much the company earns relative to the value of the listings it hosts on its platform.

It is calculated using the formula:

$take\text{-}rate=\frac{Revenue}{GMV}$

That is, you take the total money the platform received for hosting listings and divide it by the total value of all the goods and services posted on the platform.

Why is this metric needed?

This metric shows how efficiently pricing is set up on the platform, because such a platform effectively helps sell goods and services, which means its income should somehow correlate with the value of the advertised goods and services.

At the same time, if we take basic unit economics, it is in no way connected either to take-rate or to GMV. And yet the take-rate metric itself should be connected to the price, which in unit economics we describe as AOV. That's precisely why it's so important to calculate this metric correctly — because with a flawed analysis we may mismanage the platform's pricing and lose revenue from paying customers.

My questions about this metric

You'd think — what could possibly go wrong here? But it turned out that almost everything can. I had questions about every variable in this formula.

The first thing to think about is how to count GMV. On classifieds boards, listings are usually posted for free, and owners pay only for some of them in order to additionally highlight them. This is done to attract more attention to a listing amid heavy competition; owners have an interest in promotion and pay for it.

And this means that we earn not from all listings, but only from the ones that were paid for. So does that mean GMV should also be counted only from the listings that were paid for?

Next, the price of the listing itself. Imagine you're selling an apartment and you posted a listing for 100,000 c.u. (conventional units); a month later you lowered the price to 95,000 c.u. What was the GMV of that listing?

Then difficulties arise with calculating Revenue. In the classic approach, we simply take a given month for which we're calculating take-rate and sum up all the money we earned that month.

But did we correctly estimate how much we earned from a listing? After all, the listing's owner may have paid for the platform's services over several months. And if in the current month he paid us 0, but last month he paid 100 c.u., does that mean the current month's take-rate shouldn't account for his listing?

How I propose to calculate take-rate