I know you're going to get (and have already gotten) flak for your response, but I appreciate your honesty. It definitely sounds like you're trying to be responsible financially and cost of living is extremely high in the Bay Area for sure (as I've experienced myself).
Like others have mentioned though, it's very easy to get in the mindset of "When I have $x, I'll be able to give". Financial security and piece of mind for your family is obviously very important, but generally, getting to a point where you can give is more about a mindset than actual numbers. If you don't feel you have enough now to give, it's unlikely like you ever will. Not everyone can have Bill Gates money :).
I recently was in a class that taught economic discipleship at my church that worked on transforming both mind and heart to be responsible financially. This means not only giving more, but also being responsible with budgeting (accountability for own finances), giving responsibly (to responsible charities), and spending happily (being grateful for one's own wealth). One "homework" we did was to start by cutting some of the excess in our life to save money. These were very simple things like cutting out a latte a week, eating in more, driving less, etc. The actual amount itself may not have been significant to start, but it keeps you very conscientious of where money leaks, and how that money could benefit others. We then researched charities to find ones doing the most impactful work and gave some of that money we saved. We also gave a larger contribution over a longer term by designating different percentages of our salaries/bonuses as not our own, but for others.
These little steps help make giving and being aware of the need elsewhere in the world a daily part of your life rather than something that seems like a distant dream or something you do before the end of the tax year. I am by no means some giving expert, but I've been working on these very things myself with my family and hope it can help make a dent on the poverty and inequities in the world. Gates's letter gives us great hope and motivation that our efforts today and not tomorrow can and will have enormous implications for the well-being of the world's population.