Throw them in. Sometimes they disingegrate but most mostly they will come out unaffected. I wouldn't take the time to pick them out before composting. If you screen your compost, take them out then.

If you grow peaches, and you have a large amount of spoiled fruit to compost, then you could leave the pits with the peaches, and let them fall to the bottom of the pile, where they will eventually become finished compost, in a year or two. If you have a small compost pile, and only a few peaches, then you probably don't want peach pits in the pile, because they will take a long time to disappear.

In my compost and soil, peach pits last for years. But I doubt that they have any impact on fertility.

Thank you all! I have about 20 peaches. Seems like the best thing to do since I hope to use my compost within a year is to throw the seeds out. Here's another related question. I'm trying my best to keep the correct ratio of browns to greens, so assuming I'm fairly on-track with that, can you use too much of one specific green? For example, is there a limit to how many peaches (or other fruit) I should include in the compost? Thanks so much for your help! :)

I would not bother removing pits - the flesh will break down fast. When you use the compost the pits are easy to spot and toss - easier than getting the flesh removed from peach I would think.

Life is too short to remove peach pits from compost heaps. And you would lose the fun of random volunteers in your garden. I've had dates and avocados come up, even over here, although they always die come winter.

The pits of those peaches could stay undigested for a very long time, unless you somehow get moisture inside and then the pit freezes and that breaks the pit.
How many peaches to add at any one time depends on what else is put into the mix. In my 4 x 4 x 4 compost piles adding a peck of peaches at any one time would be a bit much, but that same amount added to two piles would most likely not be depending on how much other, dryer material I have available to add.

Cool! Sounds like there are several different ways to do it. :) Maybe I'll just throw in about half the peaches and leave the seeds. Mustard Seeds is right. It should be easy to remove them once everything else has broken down. :)

You needn't bother removing them even then. Your plants will grow fine around them and eventually they'll break down in the soil ... or sprout, as Flora says.

If it belongs in a compost pile, it goes in my compost pile. If I had 100 peaches, they would go in my compost pile. I can't imagine even a tumbler that couldn't handle 20 peaches.

Actually you can compost peach pits it's just slow to brake down

The ghost of a peach stone, is just an over-size mulch. Compost them peaches and over-look the stones.

As to your 2nd ? Re: green/brown ratio, unless in a hurry to use compost, don't worry about ratio, waste will decompose no matter how much/little thought and effort you put on ratios. And the idea is to let Mother Nature do the work for you witho what you have, not worry about ratios or fruit stones or spending $$ on bagged stuff when you have resources at home to make your own almost effortlessly