Free home-building viability tool
Could you build the home you want?
Put in a few rough numbers and see how selling, keeping your place, or waiting could stack up.
Free to use. No account required.
Three ways forward
Sell, keep, or wait?
See how each option stacks up.
Sell and build
Put what is left after the mortgage and selling costs towards the section and build.
Keep and build
Keep your current home in the picture, including rent, running costs, and the extra lending you may need.
Build later
See what could change if house prices, build costs, income, and savings move over time.
What you can check
The main numbers, all in one place.
Add up the whole job
Put the section, build, site works, connections, council costs, changes, and a buffer in one place.
See what each choice means
Compare selling your place, keeping it, or waiting a few years.
Check if the repayments fit
See rough monthly costs during the build and after you move in, alongside your household income.
Try higher and lower costs
Move costs and interest rates up or down to see what makes the biggest difference.
See what waiting might change
Try different house prices, build costs, income, and savings a few years from now.
Save it or share it
Start without an account, then save by email, export JSON, or invite someone to have a look.
Questions people ask
Does it cost anything?
No. couldbuild is free. There is no card, no trial period and no ads.
Do I need to sign up?
No. Start without creating an account, and keep your plans on your device only. You can create an account if you want to use it on another device or share with someone. You can also export a JSON file for a copy of your own.
Is my data private?
Yes. Until you create an account, your data stays on your device. After you save, it stays private unless you choose to share a plan with someone.
Does it connect to my bank?
No. There are no bank logins and no bank feeds. You type in the numbers you want to model, so couldbuild only knows what you tell it.
What do you do with my information?
Nothing beyond running couldbuild. It is not sold, shared for advertising, or used to target you. JSON downloads are made on your own device.
Will it tell me if I can afford to build?
It gives you a rough starting point, not an approval or financial advice. Check the numbers with your bank or broker, builder, and lawyer.
Can I model more than one plan?
Yes. You can save multiple plans and compare different pathways — sell and build, keep and build, or wait.
If your question is not here, send us a message below and we will answer it.
Your data
What happens to your data
Have a go without signing up. Your plans stay on this device until you choose to save them, share them, or export a file.
Starts on your device
The data you enter stays on your device only, until you create an account.
Save when you want
Create an account to come back on another device or share. Or export a JSON file and keep a copy yourself.
Nothing is sold
Your information is not sold, shared for advertising, or used to profile you. JSON downloads are made on your device.
See how your numbers stack up.
couldbuild gives rough estimates only. It is not lending, financial, valuation, tax, or legal advice.
Contact
Got a question or an idea?
Send a general enquiry, feature request, bug report, or privacy request.