This an interesting topic, but one I haven't looked into much. I would like to see more work on this because while some claim that the link between prosocial spending and well-being is universal (Aknin et al., 2013) I wonder if that was a bit premature .  The study I reference found cross sectional correlations between subjective well-being and prosocial spending in 136 countries and followed this up with a few small experiments that concurred. 

Some other literature in the area for what it's worth: A series of recent pre-registered experiments (n =~ 7k) found mixed results (2 positive, 1 null) on the effect of  prosocial spending (not giving exactly) on happiness (Aknin et al., 2020). Another experiment (n = 615) finds that people do not adapt to giving like they adapt to spending on themselves (O'Brien and Kassirer, 2018).  Several studies find that the degree of warm glow is increased by being informed about its impact and having a greater orientation towards "meaning and authenticity" (n = 126) (Lai et al., 2020), another found that happier giving experiences were marked by feeling as if the choice was freely chosen, has a clear impact or is made towards a cause that the giver is connected to (Lok & Dunn, 2020 ).

Chapter four of the 2019 World Happiness Report reviews some of the evidence of prosocial behavior and subjective-well being (although it does not appear to mention the studies I reference above).

Now comes the controversial line from a recent study (n = 325) that takes a different tact: "Regression results showed that saving a life decreased long-run happiness by 0.26 SD (P < 0.01) (Table 1, column 4) relative to receiving money, conditional on individual-specific baseline levels of happiness." from Falk & Graeber (2020). 

Some comments on the above study (I haven't look at it in detail): By long-run they mean four weeks and they think saving a life means saving a life. 

Under conservative assumptions, a donation of 350 euros—roughly $400 at the time—covers all costs incurred by Operation ASHA to identify, treat, and cure five more patients, which is equivalent to saving one additional human life in expectation. 

Another relevant quote from the Falk & Graeber paper: 

A positive correlation between prosocial behavior and happiness is a central empirical justifi- cation for the quest to donate more. Philosopher Peter Singer forcefully argues that altruism is not about self-sacrifice, but that the greatest happiness arises from helping other people (33).

I'm just sharing because it seems like a good norm to default towards sharing things like this, and maybe it helps someone else to do a better version.

Strongly agree that this would be a good norm. Thanks for leading by example!

At first I thought it at least indicates that people got as much satisfaction from donation as from whatever else they might have done with the money (since it's controlled for income but not income minus donations). But the median donation is $150 so not enough to make much difference in a yearly budget.

Nick Epley at UChicago and Sonya Lyubomirsky at UC-Riverside have done research on how giving causes happiness. One pithy quote is:"Lyubomirsky: The answer is very clear... The research shows that it’s generosity that makes people happier, not selfishness or self-interest." Here are a few links that popped from a short Google search.

Epley and Klein 2014 paper based on 11 experiments, The Topography of Generosity

Lyubomirsky interview