Tool to calculate cascaded but independent single-pole RC hi-pass filters
There are a billion such tools (well, that's hyperbolic, but there are many).  They may not use the exact topology you have there, but they'll all get the job done.  

TI and ANALOG DEVICES are just two chip makers that provide good design tools online, and Microchip has a downloadable program

Note that when you cascade two two-pole filters, your -3dB point for the first filter then becomes your -6dB point.  If you really want to do the math, just solve for your -1.5dB point $$ \left | H\left (j\omega_c   \right ) \right | = -1.5dB, $$ where H is the transfer function of your first stage and \$\omega_c\$ is your target cutoff.  Of course, if your caps are 20% tolerance, YMMV on what the transition region actually ends up looking like.

Still, the best way to get an optimal filter is by providing your filter specs and figuring out how many poles you need to get it given a particular filter topology, and then using a pole-placing topology to get it -- e.g., use the filter design tools the way they were meant to be used.