Here's the short answer to this question: different scoring models.

Mortgage lenders use:

FICO 2 (Experian)

FICO 4 (TransUnion)

FICO 5 (Equifax)

Online credit monitoring most likely uses VantageScore 3.0

The difference in these scoring models has different emphases on certain aspects of credit. Like higher credit card usage might impact one model more than the other.

That's the short version.

But you may have lingering questions like

Why did my score tank after a hard pull?

My answer to that is the pull itself didn't cause the score to tank.

Credit Karma, or whatever reporting service, refreshed your score.

The most likely cause: credit card balances went up.

Your old score didn't reflect that. The mortgage pull triggered the refresh in balances.

Does shopping for a mortgage hurt my score?

When you're shopping for a mortgage, you might notice that every lender wants to pull your credit. And yes, these are hard pulls.

So does that mean your score is going to tank every time you shop lenders?

Another short answer: Yes, a mortgage preapproval is a hard inquiry. But no, it should not significantly hurt your score, and you can shop around without repeated damage.

Here is how it works:

Mortgage inquiries fall under “rate shopping”

Credit scoring models understand that people shop around for mortgage rates. So when you get multiple mortgage inquiries within a short window, they are counted as one inquiry for scoring purposes.

How long is the window?

FICO 2, 4, and 5 (the versions used for mortgage underwriting): 14 days

Newer scoring models (not used for mortgages): 30 to 45 days

So if you plan to shop lenders, do all your preapprovals in the same 2-week window to keep it as one hit.

The CFPB website contradicts this and says 45 days, but again, that's for newer scoring models.

How much does a mortgage inquiry typically affect your score?

Usually around 3 to 8 points.
If your credit profile is strong, it may not move at all.
If your credit is thinner or newer, the drop can be more noticeable but still small.

What does move your score in bigger swings:

High utilization on credit cards

Late payments

Collections

New personal/auto loans

Mortgage inquiries are minor in comparison.

Can you remove the hard inquiry?

Only if it was unauthorized.

If you actually applied, gave permission, or clicked consent online, the inquiry is valid and cannot be removed.

If it was unauthorized, you can dispute it through:

Equifax, Experian, and TransUnion online dispute portals, and

The lender who pulled it (ask for a copy of your signed authorization)

The real danger is multiple preapprovals over many months

If you drag out the shopping process, you’ll restart the rate-shopping clock over and over.

This is why people see “lots of mortgage inquiries” and think they’re being harmed. It isn’t the shopping, it’s that they’re doing it over months instead of weeks.

The smartest way to shop lenders without hurting your score

Get your free credit report and score first (annualcreditreport.com + Experian.com)

Fix anything obvious (high utilization, outdated info, etc.)

Make a list of 3 to 5 lenders you want to compare

Let them all run your credit within the same 14-day period

Compare Loan Estimates side-by-side

This gives you the best shot at the best deal with one inquiry.

If you do that, you protect your score and still get the ability to compare rates.