When do you need to change the cam-belt on a 406 2.0 hdi?

I do mine (taxi fleet of 4, and formerly had year-2000 306 2.0HDi fleet the same) every 50-60thousand miles, = approximately 80,000km.

If you have just bought the car, do it anyways. Don't believe a dealer (even a main dealer) or salesman, even if they have "proof" on paper. Just do it. My last ones cost £30 parts (40 Euros) and 2 hours labour.

I do not buy genuine Peugeot ones, just a reputable brand that the garage trusts.

I think the recommended by Peugeot is something like 120,000km.

Big repair if it fails.