Stamp Duty- lower or higher?

[primarium]

DH has a property where we all live at present. It is in his sole name. We are buying bigger house, which will be our main residence. Remortgaging first property, putting it in our both names and turning it into Buy To Let.
When checking gov.co.uk SDLR calculator, it shows us we have to pay lower tax (£20,750), but our solicitors insist that the stamp duty will be £38k. No matter how many times I use that calculator(online) it gives me £20k amount, as we will be buying our main residence. I think this is so weird loophole, which I'm absolutely willing to use to my advantage.
The property we are buying is £617k.
I have no idea where to turn for advice.

you are buying a second property so you pay higher stamp duty. not sure what you are putting into the calculator.

At the end of the purchase, you will have 2 houses, so higher rate is payable

Yep, as above. You own one property, you are buying a second property, you will then own 2 properties.

3% additional SDLT applies.

@deathbollywood is correct. It’s a second residence so you will need to pay the higher amount. You can claim the additional 3% back if you sell the initial residence within 3 years

Are you answering that it will replace your main residence? The small print says If your previous main residence has not yet been sold choose "No".

So have you put no as the answer to that question? Because your previous main residence will not have been sold.

Yep, agree with other posters. If you were selling your first residence you’d have the 20k to pay as you’re moving from one main residence to another, but as you’re buying an additional property it’s the £38k.

Yes you have to pay the higher rate because you are not selling your current main residence. This is what the government website says:

‘If you’re replacing your main residence
You will not pay the extra 3% SDLT if the property you’re buying is replacing your main residence and that has already been sold.

If you have not sold your main residence on the day you complete your new purchase you’ll have to pay higher rates. This is because you own 2 properties.

You can apply for a refund if you sell your previous main home within 36 months.”

This is the important question. You must answer no to the second question as you haven't sold the previous property.

Even if it's going to be your main residence you'll have 2 properties at the end of it.

If you sell the original property within 3 years you may get a refund.

If it is replacing your main residence you wont pay higher stamp duty.

‘Replacing’ in this case means selling. So if you’re replacing by selling, yes you pay lower stamp duty, if you’re replacing but not selling, it’s the higher.