This guide walks you through everything you need to add a Plan 58 calculator to your own website, from signing up for a free trial to handing the code to your web developer and customising how it looks.
What does "embedding" mean?
When you embed a calculator, a small piece of code is placed on your website that loads the calculator inside a seamless window (called an iFrame). Visitors on your site use it without ever leaving your page. The calculator lives on our servers, you don't need to install anything and it updates automatically.
Step 1 — Activate your free trial
You start the process directly on the calculator's own page on our website.
Scroll down to the "Capture leads with the [Calculator Name]" section.
Enter your website address (e.g. mywebsite.co.uk), just the domain, not the full URL.
Enter your email address. This is the address that will receive leads from visitors (you can change it later) and will be used to log in to the Customer Portal.
Click Activate Free Trial.
Your 7-day free trial starts immediately. No credit card is required to start.
The system automatically strips out anything you don't need — so whether you type https://www.mywebsite.co.uk or just mywebsite.co.uk, it will be accepted correctly.
Step 2 — Verify your email address
After activating, check your inbox (and your spam folder) for a verification email. Click the link inside it.
The link expires after 24 hours. If it has expired, go back to the calculator page, re-enter your domain and email, and click Activate Free Trial again — a fresh link will be sent.
If you entered the wrong email, follow the same process with the corrected address.
Why is this required? Email verification confirms you own the inbox that leads will be delivered to. The embed code also becomes available in the Customer Portal only after verification.
Step 3 — Get your embed code
Once your email is verified, you can log in to the Customer Portal at /customer-portal/ on our website.
Logging in:
Go to the Customer Portal page.
Enter the email address you used when registering.
Click Send me a login link — a secure link will be sent to your inbox (valid for 15 minutes).
Click the link in your email to open the portal.
Finding your embed code:
Your registered calculators are shown on the dashboard. Click the one you want to embed.
Under Installation, you will see a short code snippet — it looks something like this:
html
<script src="https://plan58.co.uk/embed.js"
data-calculator="retirement-income"
data-domain="mywebsite.co.uk">
</script>
Click Copy to copy it to your clipboard.
Keep this page open — you'll come back to it to adjust settings.
Step 4 — Add the code to your website
This step is where you (or your web developer) paste the snippet into your website.
If you have a web developer: Send them the copied snippet and ask them to paste it into the HTML of the page where you want the calculator to appear. They don't need access to your Plan 58 account — the snippet is the only thing they need.
If you manage your own website (e.g. via a website builder): Most platforms have a way to add custom code to a page. This is usually labelled something like:
"Custom HTML block" or "HTML widget" (Wix, Squarespace, Webflow)
"Custom Code" or "Embed" (Wix, Squarespace)
"HTML" block (WordPress with a page builder)
Paste the snippet into that block and save/publish the page.
Important: The snippet must be placed on a page on the same website domain you registered (e.g. if you registered mywebsite.co.uk, the snippet must appear on a page at mywebsite.co.uk). It will not work on a different domain.
A note on sizing — worth sharing with your developer: The calculator is designed to fill 100% of the width of whatever container it is placed in, and its height adjusts automatically as the visitor interacts with it (for example, as results appear). This means:
If it is placed in a narrow column (e.g. a sidebar), it will shrink to fit — which may not look ideal. A full-width content area or a centred column of at least 480px works best.
You do not need to set a fixed height — doing so may cause the calculator to be cut off. Let the container grow naturally.
The calculator is fully responsive and works on mobile, tablet, and desktop screens without any extra configuration.
If you are unsure how to set up the container, a simple approach is to place the snippet inside a standard full-width section or content block on your page and let the calculator handle the rest.
Customising how the calculator looks (optional)
You can adjust the calculator's colours and corner roundness to better match your brand. These settings are in the Customer Portal under Appearance.
Setting What it does Example value
Primary / accent colour Buttons and highlights #1d4ed8
Background colour The calculator's background #f8fafc
Border radius How rounded the corners are 12px or 0.5rem
Colours must be entered as hex codes (the # followed by 6 characters format you can get from any colour picker). Changes take effect on your website immediately — you do not need to update the embed code or ask your developer to do anything.
Click Reset to default at any time to remove your customisations.
If you're working with a designer or developer, they can find the correct hex codes from your brand guidelines.
Managing lead notifications
When a visitor fills in the lead capture form at the end of the calculator, their details are emailed to the address you registered with.
In the Customer Portal under Lead notifications, you can:
See which address is currently receiving leads.
Update the delivery address. Changing it sends a verification email to the new address — your current address keeps receiving leads until the new one is confirmed.
You can also use the Display settings section to toggle the lead form on or off entirely, and to show or hide the assumptions section that explains how the calculator's figures are calculated.
Billing and subscriptions
Your free trial lasts 7 days. After that, a subscription is required to keep the calculator live on your website.
In the Customer Portal, under Billing, click Subscribe to start a paid plan.
Billing is handled securely via Stripe — your payment details are never stored on our servers.
To manage invoices, change your payment method, or cancel, click Manage billing, which opens the Stripe customer portal.
If you cancel, the calculator will stop working on your website at the end of the current billing period.
Troubleshooting
The calculator isn't showing on my website.
Check that the embed code is on the correct page and that the domain matches exactly what you registered.
Confirm your email has been verified.
Check that your trial or subscription has not expired (log in to the Customer Portal to check).
I didn't receive the verification email.
Check your spam or junk folder.
Return to the calculator page, re-enter your domain and email, and click Activate Free Trial again to receive a fresh link.
I entered the wrong email address.
Return to the calculator page, re-enter your domain and the correct email, and click Activate Free Trial again. If your email has not yet been verified, the address will be updated and a new verification link sent to the corrected address.
The calculator appears but shows an "expired" message.
Your trial has ended or your subscription has lapsed. Log in to the Customer Portal and subscribe to reactivate it.
My colours/theme aren't showing correctly.
Colours must be entered as valid hex codes starting with # (e.g. #1d4ed8). Colour names like "blue" are not supported.
Border radius must be a number followed by px, rem, or em (e.g. 12px).
The calculator looks too narrow, is being cut off, or isn't filling the page properly.
The calculator fills 100% of its surrounding container. Check that the container on your page is not set to a fixed, narrow width.
Do not set a fixed height on the container — the calculator adjusts its own height automatically. A fixed height on the wrapper <div> or a CSS overflow: hidden setting are common causes of clipping.
If your page builder has added extra padding around the embed area, ask your developer to reduce it.
I need to embed the calculator on a second domain.
Each domain needs its own registration and subscription. Return to the calculator page and repeat the process with the new domain.