If it costs $4000 to prevent a death from malaria, malaria deaths happen at age 20 on average, and life expectancy in Africa is 62 years, then the cost per lifetime saved is $0.0109/hour.
If you make the average US income of $15.35/hour, this means that every marginal hour you work to donate can be expected to save 1,412 hours of life, if you take the very thoroughly researched, very scalable, low-risk baseline option. If you can only donate 10% of your income, then your leverage is reduced to a mere 141.2. Just by virtue of having been born in a developed country, every hour of your time can be converted to days or weeks of additional life for someone else.
While not as insanely huge as some of the figures making the argument for longtermism, I find this figure more shocking on a psychological level because it’s so simple to calculate and yields such an unexpected result. This type of calculation is what first got me interested in Singer-style EA.