In a large, deep stainless steel saucepan, combine peaches and lemon juice. Break up peaches with a potato masher. Whisk in pectin until dissolved.
Bring to a boil over high heat, stirring frequently.
Add all of the sugar and return the peaches to a boil while stirring constantly. Boil hard, stirring the whole time, for 1 minute. Remove from the heat and skim off foam.
Ladle jam into hot jars, leaving ¼” headspace. Remove air bubbles and adjust headspace as needed. Wipe rim, center lid on jar, and screw down the band until it is fingertip-tight.
Place jars in canner, making sure they are completely covered with 1” of water. Bring to a boil and process for 10 minutes. Remove canner lid, wait 5 minutes, and remove jars. Cool and store.