Java/Html help

You can do the whole thing in javascript, so it runs on the visitors computer. This way you won’t have to deal with passing values.

Or, you can use ajax to grab the answer from a script and change the page accordingly.

Otherwise…

WordPress pages are in html, it just looks a lot cleaner to not include that part. If you wanted to, you could.

Also, the url parameters (after the ?) aren’t necessarily related to not changing the URL.

Here is the problem.

Go to the WordPress Settings->Permalinks and you will see that wordpress works by passing values via url parameters like ?var=value&var2=othervalue. The default permalinks settings is https://example.com/?p=123.

WordPress just takes the values after the ? in the url to find pages. Then, the permalinks settings takes those urls and converts them into the pretty urls that we are used to seeing.

WordPress is probably trying to use your values to find a page. They don’t make sense so you get a 404.

You should modify the form, and the script that accepts it, to use POST. This way, it won’t interfere with wordpress.

You can avoid changing the URL by including the logic in the form.

Like this (but replaced with real code ^_^)

/** BMI page **/

If post variables exist {
Calculate and display stuff about BMI
}
Else {
Display BMI calculator form with the POST method
}

If I’ve made any errors I please let me know