# Estimating the % of people who make 1-off purchases in a single year

Market sizing
New answer on Dec 05, 2022
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Hello,

For market sizings involving one-off purchases, like estimating the size of the lasik surgery market in the UK, it is easy to reach the total potential market for lasik surgery (i.e., the market size if everyone who wants and can afford to get lasik surgery gets it), BUT realistically, not everyone will get it in a single year and some might delay their surgery to subsequent years. Is there a way to robustly estimate the % that gets it in a single year? I have been struggling to come up with a strong reasoning to back up a number.

Thank you!

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Hi there,

This is a replacement rate type question!

As in, if we're doing the car market, we would need to assume an average person replaces their car every x years (let's say 10). We then divide the total # by 10 to get the market size (an annual revenue).

For Lasik, you need to do the same. So, of the people that *would* get Lasik, then how many *will* get Lasik, then *how often* in a lifetime will they get it?

Hello,

The way I would simplistically approach this is as follows:

Lets assume that there are 1 Million people in our reachable market (those who need it and those who can afford it).

Also, assume that LASIK is allowed for people between the ages of 18 to 60.

That means, those 1 million people have ~42 years to do LASIK in their life.

Thus, our yearly market will be 1M/42 = ~24K customers

Caveat: This is a very simplistic approach and you should factor in birth rates, death rates, etc as well.

All the best!

Rushabh