The general answer is “as much as you can” and while this is true we know it’s not very helpful, so here is our, more nuanced, answer:
First, before you even think about investing, make sure you have a handle on your budget. Any money you invest should be money you have saved. Do not go into debt to invest when you are just starting out.
Next, you want to build an emergency fund which has enough money to cover 3-6 months of expenses. You should hold this in a liquid and low-risk place like a high yield savings account so you can access the money whenever you need it.
Once you have a plan in place for your budget, then you can figure out how much to invest. No amount is too little, though we do suggest you start with at least $100 so you can buy a diversified portfolio of stocks.
Remember, the earlier you start investing, the better. When you invest for the long term, compounding grows your money exponentially. For example, by the time you’re 60, the money you invest in your 20s will likely be worth as much as the money you invest in your 30s, 40s, and 50s combined.
No matter how much you decide to invest, congratulations for getting started!