Privacy

Cost My Extension is run by Oliver Davidson, trading as Cost My Extension, who decides how your personal data is used and is responsible for it under the UK GDPR and the Data Protection Act 2018. Write to [email protected] about anything on this page. The postal address is in the terms.

We never ask for your name. What we do hold:

The property and your answers

The postcode and address, the type of house, the job you have in mind with its size, finish and timing, and anything you write in the notes box. If you buy as a professional, the name of your practice.

Your email

To send your report, your receipt and the few emails listed in section 05.

The free check

If you ask for the full free check by email: your email, the address, the house type and job you chose, and the result we showed you.

Payment

Stripe tells us that you paid and when. We never see your card details. We also record the moment you ticked the box asking for the report at once, because consumer law asks us to be able to show it.

Feedback

Your answer to the one question we ask after a report, and anything you add.

Your IP address

Used to deliver the site to you and, held in memory for no more than a day, to stop the free check being run thousands of times by a script. It is not stored in our database.

Your report sits at a private link that is not listed anywhere, but anyone you give the link to can read it. Please do not put anything about your health, money or other private matters in the notes box: the report does not need it. If you buy a report for a client, please tell them their address and details are being used to produce it.

The law asks us to name the legal basis for each use.

To produce and deliver what you ask for

Writing and sending the report, writing it again when you change your answers, refunding it if it cannot be written, and sending the free check. Basis: the contract between us.

To keep records of sales and refunds

Including the time you agreed to immediate delivery. Basis: our legal duties under tax and consumer law.

To run and improve a small business

The one reminder and the one feedback email, counting visits, and keeping the site safe from abuse. Basis: our legitimate interests, which we have weighed against yours. You can object at any time, and we will stop.

The report is produced automatically, but it is an estimate for you to read. It makes no decision about you.

A few providers run parts of the service for us. They act on our instructions under data processing terms and may not use your data for their own purposes. Stripe is the exception: it is also responsible in its own right for the payment details it collects.

Anthropic

Its AI model, Claude, writes the wording of the report. It receives your answers, the address and the public facts about it, but not your email. Under its commercial terms Anthropic does not train its models on this data.

Stripe

Takes the payment. It receives your email and what you are paying for, and its own privacy policy covers your card details.

Resend

Sends our emails, so it receives your email address and what each email says.

Supabase and OVHcloud

Host our database, in London, and the server the site runs on, in Europe.

Cloudflare

Sits in front of the site to deliver it and protect it from attacks, so it sees the requests your browser makes, including your IP address.

Public registers

To look up the property we send the postcode to postcodes.io and the Energy Performance Certificate register, and the map position of the property to planning.data.gov.uk. They receive nothing else about you.

Anthropic, Stripe, Resend and Cloudflare are based in the United States and may handle data there. Where they do, the transfer is protected either by the UK's data bridge with the United States, for providers certified under it, or by the international data transfer terms approved by the Information Commissioner, which are part of their data processing terms.

We do not sell your data, and we do not share it with anyone for their marketing.

About your purchase

The receipt, the link to your report when it is ready, and a notice if we refund it.

The free check

The link to your full free check, if you asked for it.

One reminder

If you give your email and see the preview but do not buy, we send one reminder the next day. It has a link to stop any more.

One question

A day after your report we ask once whether it was useful, and keep your answer with the report.

There is no newsletter and no other marketing. To stop either, tick the box under the email field when you give it, use the link in the reminder, reply to the email, or write to us.

Paid reports

The report, the answers behind it, your email, the payment record and your feedback: six years from purchase, as the tax rules on business records require, then deleted automatically.

Enquiries never paid for

Twelve months, then deleted automatically.

Free-check requests

Twelve months, then deleted automatically.

Logs and backups

Server logs, which note which address an email went to, are kept for up to 30 days. Backup copies of the database are kept for up to 90 days, so a deleted record leaves the backups within that time.

Stripe keeps its own payment records for as long as its legal duties require.

This site sets no cookies of its own and stores nothing in your browser. To count visits we use Umami, which we run ourselves: it records the page, the site that sent you, the type of browser and device and a rough location, without cookies and without keeping your IP address, so no one can be followed from one visit or site to the next. Cloudflare may set a cookie it needs to tell people from automated traffic, and Stripe's payment page uses its own cookies, which Stripe's policy explains.

You can ask for a copy of what we hold about you, have it corrected or deleted, ask us to stop or limit how we use it, or have it in a form you can take elsewhere. Write to [email protected]. We reply within a month and there is no charge. If you ask us to delete a paid report, we delete it, but may keep the bare record of the sale for as long as the tax rules require.

If you are unhappy with how we have handled your data, please tell us first. You can also complain to the Information Commissioner's Office at ico.org.uk/make-a-complaint or on 0303 123 1113.

If what we do with your data changes, we will update this page and the date below. Last updated 20 October 2026.