How long should MTB disc brake pads last?

The Strathpuffer race ( a 24 hour MTB race in Scotland in January) is famous for grinding down brake pads in one night. The year I did it, I replaced the brake pads twice during the 24 hour period. Its something to do with the mud at Strathpeffer turning into a grinding paste that just eats the brake pads.

Saying that though, in everyday use, a set of brake pads last me a season.

I'm fairly new to mountain biking. However, I have been riding using my Avid Elixir 3's since August last year and have only had to change the pads this week having done 25-40 miles every week. So I think in such short time you have not done so well with your pads. I hope I helped.

I've made 1700 km before I changed my pads (just rear - front pads are still OK, at about 50%). I had resin pads and now I have switched to sintered metal - so far not too loud, but braking force is better.

I have Shimano BR-M395 hydraulic brakes, and IMHO they are great (not perfect, but in city - more than enough for me).

I have Promax Decipher Hydraulic brakes and I have sintered metal brake pads. I have roughly done about 1000 miles in last 6 months. My brake pads are still fine. It seems like they will probably do another 800 miles without a problem. I had these other mechanical disc brakes and their brake pads finished under 100 miles. I changed the rotor and the calliper and after that no problems. I would suggest you to do the same. Hope that helps.

To add one more data point - I have a Trek FX Sport 5 that I bought a little under a year ago. Been riding 50-250 miles per month on it, call it 1800 miles since purchase, and I just had the pads wear out. My normal ride is a 500ft elevation change, with the majority of the elevation change within a half mile stretch.

Edit: Sorry, just realized this post was specific to mountain bikes. I'm riding a hybrid bike on pavement, not offroad. Sorry!

if I am ridding at my local trails a can get about 600 miles out of my metallic pads, but if I go to the dh park I will only get about 80 miles out of them and go though about 3 sets of pads on the front and 2 sets on the back in a weekend.

Another data point:

I ride in the North Shore of Vancouver, BC, Canada, which is an area famous for its rough, steep, and technically challenging trails. I got ~800km out of my front brake pads. At that point, the rear still had a millimeter of pad remaining or so.

The answers here are mostly about mountain biking - and the question text too - but the title is general and the question will be found by people riding other kinds of bikes.

On my gravel bike with the default TRP pads on TRP Spyre brakes I made 6500 km and I am now nearing the 0.8 mm thickness limit. That is considerably more than what people indicate here for mountain bikes.

Many of those kilometers were on the road but many were on forest trails. Do take into account that TRP pads are hybrid resin/metal. Pure resin pads may last much less (and will be cheaper).

I typically ride 50 miles per week with 8,000 to 10,000 ft of descent (and ascent). I get about 200 miles out of a pair of pads. (SRAM Centerline 200 mm rotors and resin pads.)

Although not for MTB, but for road: my front resin K03S pads wore out in 2000 km. 99% braking with front brake and 1% with rear brake.

I have a theory that hard braking could cause more pad wear. I found some studies about correlation of pad wear and rotor temperature, and it seems high rotor temperature (hard braking) causes more pad wear. Also, I found a study about drum brake lining wear in trucks and buses, and it seems long distance buses that brake less but harder (2x as hard) than city buses see far more pad wear, so much that for the same amount of braking, hard braking causes 2.5x times the pad wear that easy braking would cause.

I have a rather sporty riding style, braking as late as possible, as hard as possible, to increase my average speed. However, recently I calculated one brake application late and hard causes only 0.3 second time savings compared to easy and early braking, and that the value of my time that I save by braking hard is about third of the cost of the additional brake pad wear it probably causes (assuming the 2.5x coefficient that was valid for bus drum brake linings is valid for bicycles too). So I have to reconsider my riding style.