Is Extreme Power Supply Calculator Pro accurate?

I'm trying out the Extreme Power Supply Calculator Pro and it gave out a result of Minimum PSU Wattage: 379 Watts, Recommended Wattage: 429 Watts. Is this accurate? I have a desktop that has an Intel i5 processor, 4 GB RAM, 1 GB GeForce Video Card, 1 TB HDD and a generic 500 watt power supply unit.
