Why 10%?

Because that's the number of the 10% Pledge. No other reason.

How big a deal is donating 10% of your pre-tax income really?

On the one hand, 10% of one's income feels like a lot of money no matter how much you make. But on the other hand, incomes vary tremendously such that no matter how much you make, giving away 10% of your income won't change your relative income rank by much.

If you're an American who income is higher than 20% / X% / 80% of Americans, then your effective income leftover after donating 10% of your pre-tax income will still be higher than 18% / X-7% / 76% of Americans.

In the US, donating 10% at most lowers your income percentile by 6.3 percentile from 54th percentile to 47.7th percentile, requiring you to live on $49,500 instead of $55,000.

So from this perspective at least, it's clear that donating 10% is not that a big a deal.

Yet, of course, your 10% can be a huge deal to the world or the recipients of your charity.

An old related memory

On Giving Tuesday, November 27, 2018, Facebook hosted a counterfactual donation match in which they gave away $7 million to the nonprofits users donated to on a first-come, first-serve basis with some limits. Hundreds of EAs participated and collectively we directed about $469,000 in Facebook's matching funds to our preferred EA nonprofits that year.

That night, I was at a friend's house for dinner with several other friends. In the course of relaying the story of how the match went (there were a fair amount of logistics), it came up how much I personally donated. One friend asked "Why'd you need to make eight separate donations?" and I explained (paraphrasing) "Facebook had a size limit on donations of $2,500, but an individual match limit of $20k, so in order to get the maximum match amount you had to make eight separate donations."

I was in my early 20s and this was a lot of money for me and well over 10% of my income for the year, but I was excited to take advantage of the matching opportunity while it existed. (Later I found out that I got all $20k matched.) So my friend was like "You donated $20,000?" and I was like "Yeah," and then he said "Wow, that's a lot" or something in a way that led to awkward silence in which I wasn't quite sure what to say (or so my memory goes).

His reaction and what I thought to myself next is what sticks in my memory. Something about his tone made me feel like he was judging me. If I had said I had bought a car for $20,000, he certainly wouldn't have reacted "Wow, that's a lot of money." It was clear he was thinking that it was a lot of money to give away.

I recall thinking to myself that yes, it's a lot of money, but also, he's a software engineer who probably makes over twice as much money as me, so is it really a lot of money to donate? He could donate that much and still have much more remaining income that year than I earned pre-tax. Also, at least one other friend at the table made less money than me even after subtracting the amount I donated. So in the grand scheme of things, it's not like it was a big sacrifice or anything. It just meant I'd have less savings in my bank account. To me, it seemed like a perfectly reasonable amount of money for me to donate, but I didn't have the words to articulate why at the time and just felt awkward.

Better versions of this chart

I hadn't seen a chart like this before despite thinking of the idea of it several times over the years, so I decided to just make one. If you feel like making a better version than my MS Paint image, share it in the comments! Here's the data I used. It may also be cool to plot the values for donating e.g. 20%, 30%, 50% on the same chart.