How Much Power Supply Headroom Do I Need?

_Mutant

Honorable
Oct 15, 2015
57
0
10,640
In general what is a good rule for how many watts you need extra for the build to run smoothly

I was thinking about upgrading my CPU and GPU but I really don't want to upgrade PSU at the same time so I wanted to know how much headroom is enough for any build. Just a rule of thumb.
 

_Mutant

Honorable
Oct 15, 2015
57
0
10,640


Current Build:
Pentium G3258
16GB of RAM
EVGA GTX 750 TI
MSI H81M-E34 Motherboard MATX
Corsair 200R
WD Caviar Blue 1TB HDD
CoolerMaster Hyper T4 CPU Cooler
Corsair CX430 Watt Power Supply
Generic LG Optical Drive

Proposed Upgrade:

i5 4590
16GB of RAM
EVGA GTX 960 SSC ACX 2.0+
MSI H81M-E34 Motherboard MATX
Corsair 200R
WD Caviar Blue 1TB HDD
CoolerMaster Hyper T4 CPU Cooler
Corsair CX430 Watt Power Supply
Generic LG Optical Drive