How much is the worth of my pension that I would forfeit when leaving the company before the pension is vested

The vesting period is 5 years. If I leave the company one year short of that, what would have been the worth of the pension that I am walking out of. I am trying to get an idea so I can work this in the offer from the new employer. I hear there is some kind of formula to calculate this.
How much is the worth of my pension that I would forfeit when leaving the company before the pension is vested
I think that%26#039;s different for every company. I know in my case, I left a company after I was vested but before the next tier, so I lost out a little. But 5 years later I checked on it, and they had totally %26quot;readjusted%26quot; the pension program to reduce the payments, which apparently is perfectly legal to do, and they are now saying that by the time I retire, they may do away with the pension plan altogether, and we would all be screwed. I had no idea they could just back out on this stuff. I wish I hadn%26#039;t stayed around as long as I did!