Is there a "cleaner" way to make graphs from an equation/calculation, rather than using columns filled with data?

Out of curiosity, I want to make a graph showing progressive tax rates. I'm able to do this by creating calculated columns of data and making a graph from that (which is sufficient), but I was wondering if Excel has any way of entering a equation or calculation and making a graph from that.

(If not, any basic software recommendations that might be more appropriate?)