Help calculating monthly power draw and cost?

Would anyone mind verifying my math here? I'm trying to estimate the cost of mining for a month under the following assumptions. This would exclude the cost of other onboard system components (I'm running it from my personal desktop).

Assumptions:
-My CPU draws 84W TDP, and my GPU 150W TDP
-I run my system 24 hours/day x 30 days and try to keep things as cool as possible
-local electricity price is $0.1196/kWh

234W of drawn power x 24hrs = 5,616 watt-hours

5,616 watt-hours x 30 days = 168,480 watt-hours-days

168,480 watt-hours = 168.48 kilowatt-hours (kWh)

168.48 kWh x $0.1196/kWh = $20.15

Roughly $20 bucks added to my power bill for a month straight of Z-cash mining? Is this a realistic number or am I off by orders of magnitude? Also am I forgetting any major factors? Perhaps a minimal additional contribution from the increased power draw of my cooling fans...

FWIW your math looks correct to me.

Thank you kindly sir.

what gpu are you using that it only uses 150W ? You forgot the W for disk,Psu,motherboard and monitor.

Nvidia GTX 1070. I leave the monitor off unless checking in. Do those other components you mentioned draw significantly more power when mining as well?