Do anyone knows about any online GST Rebate calculator for buying new homes ?

I tried CRA website, there are bunch of information on GST rebate
but no Calculator

What formula they use for calculating this rebate ?

I found following website, but not sure if this is true

http://www.rodfriesen.com/gst-rebate-calculator.html

Since in Alberta, I need only GST information

For ex - House price $415000, GST rebate is $2205
Now for Home Price $425000, GST rebate is $1575

Is that means GST rebate decreases as home price increases

Thanks..