12 trees in ANOTHER country. Why? Why plant the trees somewhere else? I already grow a lot of trees-about 60 acres of natives like oak, redbud, and cedar, some pecan and a few pine, plus brush, meadows of native grass and pasture grasses, etc. There's probably more than 300 trees on my place. I want to plant a few more fruit trees (apple and pear) and a few ornamentals like redbud and dogwood.
My footprint is less than 1/2 the average for my country, already, without counting the trees.
Also, if you can point me to the best footprint calculator, especially one that allows me to put in good things I already do, I'd appreciate it! Thanks!

ABSOLUTELY NOT. This business of paying someone for carbon footprints is a scam, a scam benefiting Al Gore and other con-artists. Stop feeling guilt that someone else is laying on you.

You may have answered your own question: because you are already growing a large number of trees on your own property. Perhaps the logic of the calculator you used assumes that suggesting you grow more trees in your own area is moot. If you pay to grow trees elsewhere, you 'spread the love' around.

This is only a guess, of course.

I have to say; I am baffled by the suggestion in other answers that this is a 'scam'. You may not believe in it, but calling it a "scam" implies that someone gains money from it. If the calculator said "Send money to this website to offset your carbon" -- then yeah, it might be a scam.

HMMM - all the carbon footprint crap is created by people in Humongous buildings heated and cooled to very comfortable levels, very well lit, have high ceilings and HUGE lawns that have to be watered and mowed with the most polluting engines on the planet by illegals from another country.

Then its promoted by people who live in 4000 square foot homes or bigger, use TONS of energy shooting film and tv shows, and make movies that are shown in very cooled high-ceiling buildings that have parking lots that destroyed hundreds of trees and ecosystem resources.

When they get real. I will! Sorry, I guess this means I dont have an answer for you. Thanks for not mowing your trees.