The IRS will send a notice to explain it for you. Sometimes they may make adjustments on their own, but they will let you know why. Per IRS Topic 152 "If you receive a refund to which you're not entitled, or for an amount that's more than you expected, don't cash the check until you receive a notice that explains the difference; then follow the instructions on the notice." 

You can find details on that here https://www.irs.gov/taxtopics/tc152.html as well. 

My tax refund was way more than expected. What do I do?

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@Sunshineebea  wrote:

My tax refund was way more than expected. What do I do?

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You will receive a letter in the mail from the tax authority that issued the tax refund which will explain why the refund was changed from the amount entered on your tax return.  The letter usually is sent approximately three weeks after the refund is received.

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@Sunshineebea  wrote:

My tax refund was way more than expected. What do I do?

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Also see IRS Tax Topic 152 - https://www.irs.gov/taxtopics/tc152

If you receive a refund to which you're not entitled, or for an amount that's more than you expected, don't cash the check. For a direct deposit that was greater than expected, immediately contact the IRS at 800-829-1040 and your bank or financial institution. If you receive a notice from the IRS explaining an adjustment to a refund amount, you should do as instructed in the notice. For information about returning an erroneous refund, see Topic No. 161.

DO NOT CASH THE CHECK!!!

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@Sunshineebea  wrote:

My tax refund was way more than expected. What do I do?

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Federal or State?  If you have a tax due on one return it will not be deducted from the refund.  You have to pay a tax due yourself.  Turbo Tax just shows you the net combined amount.  How much is more?  The IRS has been adding interest on refunds.