How to migrate from Excel to CRM without losing data

What to take away

Keep the original Excel file untouched as the master copy until the CRM import is reconciled.
Clean duplicates, stale addresses and unproven consent before import, not after.
Map every field you depend on, then export a test batch back out of the CRM before the full load.
Data protection law requires accurate records and a defined retention period, so delete what you cannot justify.
HMRC record-keeping duties continue after migration, so the tool changes but the retention period does not.

Most losses start in the spreadsheet

Most reported data loss is not a CRM failure. It happens when a firm imports an uncleaned file and overwrites the only reliable copy.

Where data loss happens

Uncleaned Excel file imported
Importer cannot interpret inconsistencies
Only reliable copy overwritten
Data loss reported

Spreadsheets hide inconsistencies that an importer cannot interpret. One column may hold a mobile number and a note, while a second tab uses different headers for the same field.

Copy the workbook and freeze it

Save a dated, read-only copy, such as contacts-master-2026-03-01.xlsx, and store it where staff cannot edit it. Work from that copy, never the original.

Freeze and export safely

Save dated read-only copy
Store where staff cannot edit
Export one tab at a time as CSV
Row leaves only when CRM record confirmed

Export one tab at a time as CSV, because most CRM importers handle a single flat table better than a workbook with formulas, merged cells and hidden columns.

Set one rule: a row leaves the spreadsheet only when the matching record is confirmed in the CRM.

This is the reversible pilot approach in our guide to implementing a small business CRM, which also covers proving the export route.

Clean the file in a fixed order

Work through these steps on the copy, and count rows before and after so the import can be reconciled later.

Remove exact duplicate rows, matching on email address first, then company name and postcode.
Drop rows with no contactable detail unless a lawful reason to keep them exists.
Standardise postcodes, phone numbers and county names to one format each.
Split full names into separate columns only where the CRM requires it.
Record the date and basis for marketing consent, and remove anything you cannot evidence.
Save the cleaned data as a new file, leaving the frozen original untouched.

Cleaning first costs less than repairing thousands of records later, as our CRM data cleaning checklist explains.

Decide what each field is for

Agree what happens to each type of column before you import anything.

Field	Action before import	Reason
Email address	Validate the format and remove unused role accounts	Bounces and dead inboxes distort reporting
Marketing consent	Keep only records with a dated basis	You must be able to evidence permission
Free-text notes	Read, trim and remove sensitive detail	Limits exposure if the CRM is breached
Dormant contacts	Archive outside the CRM or delete	Storage limitation applies to every system
Phone numbers	Convert to one international format	Prevents duplicates on later imports

Import a sample of 50 records first. Check the mapping, export those records back out and compare them against the frozen spreadsheet. Load the rest only when the sample matches.

Data protection duties do not pause

Under the UK GDPR, personal data must be accurate and kept no longer than necessary. That covers the spreadsheet, the import files and the CRM.

The guide to the UK GDPR explains these principles and the accountability duty to show how you meet them.

The retained EU GDPR text on legislation.gov.uk sets out the accuracy and storage limitation principles in full, in the UK GDPR contents.

Restrict access to the migration folder, delete staging files once the load is verified, and note who approved the final import.

Keep records for the retention period

Moving to a CRM does not shorten your record-keeping duties. HM Revenue & Customs publishes the guidance on records businesses must keep, and VAT-registered firms generally keep them for six years.

Build the review date into the CRM as a field, so dormant contacts are checked on a set date rather than lingering.

If a customer asks for deletion, you must find every copy, including a CSV left on a laptop.

Common questions

Will I lose records during migration?

Not if you keep the frozen spreadsheet and reconcile counts before the team switches over. Check the row totals and spot-check 50 records. If the numbers differ, fix the mapping first.

How long does an Excel migration take?

A single table of a few thousand contacts usually needs a day of preparation and an afternoon of checking. Files with several inconsistent tabs take longer, mainly because of cleaning and mapping.

Do I need new consent to move contacts into a CRM?

No. Moving data between systems you already control does not create a new purpose, so the lawful basis stays the same. Marketing use still depends on the permission you hold and can evidence.

Can I keep some records in Excel?

Yes, if you have a clear reason and can name which records. Leaving the same contacts in both places is what creates the mismatch you are trying to avoid.