How to add a calculator to WordPress
WordPress gives you a Custom HTML block for exactly this: raw markup the editor leaves alone. That one block is all you need to drop a live, working calculator into a post or page — no plugin to install and nothing to maintain.
Step by step
Pick a tool and copy its embed code
Open the Plainso tool you want on your site and copy the one-line iframe snippet from its embed section.
Open the block editor
Edit the post or page where the calculator should appear. WordPress' block editor is where you add it.
Add a Custom HTML block
Click the + inserter, search for “Custom HTML”, and place the block where you want the calculator.
Paste the snippet and preview
Paste the iframe code into the block. Click Preview to confirm the calculator renders before you publish.
Publish or update
Save the page. The calculator is now live and interactive for every visitor.
What it looks like embedded
Good tools to embed on WordPress
Good to know
- Use a Custom HTML block, not a Paragraph block — WordPress strips iframe tags pasted into normal paragraphs.
- On the Classic editor, switch to the Text tab (not Visual) before pasting the snippet.
- A few security plugins strip iframes from content; if the block renders empty, whitelist plainso.com in that plugin.
Frequently asked questions
Quick answers before you start.
Do I need a WordPress plugin to add a calculator?
No. The Custom HTML block is built into WordPress and accepts an iframe directly. A plugin only makes sense if you want the calculator managed from the dashboard, which Plainso does not require.
Why is nothing showing after I paste the code?
Usually one of two things: the code went into a Paragraph or Code block instead of a Custom HTML block, or a security plugin is filtering iframes. Move the snippet to a Custom HTML block, and check the plugin's iframe settings.
Will the calculator work with my WordPress theme?
Yes. The calculator renders inside an iframe, so your theme's CSS never touches it, and the calculator's own CSS never leaks into your site. It stays isolated and keeps working through theme updates.