I check my 1040 and how I calculate my modified adjusted gross income

MAGI is calculated differently, depending upon the purpose. Where exactly are you being asked for this?

I want to use this to calculate the Roth IRA Limits

In order to calculate your Modified Adjusted Gross Income (MAGI), you will begin with your Adjusted Gross Income (AGI) from your Tax Return: Form 1040 Line 7.

To view your Tax Return before filing, login to your return and go to Tax Tools>>Tools>>View Tax Summary.

Next, you will add the following things to your AGI in order to come up with your MAGI : 

• Student loan interest
• One-half of self-employment tax
• Passive loss or passive income
• IRA contributions, taxable social security payments
• The exclusion for income from U.S. savings bonds
• The exclusion under 137 for adoption expenses
• Rental losses
• Any overall loss from a publicly traded partnership

If you don't have any of the above items, then your MAGI will simply be the same as your AGI.

Check out this TurboTax Article for more details on: What is the Difference Between AGI & MAGI?

But see this if you mean MAGI for ACA insurance:
<a rel="nofollow" target="_blank" href="https://obamacarefacts.com/modified-adjusted-gross-income-magi/">https://obamacarefacts.com/modified-adjusted-gross-income-magi/</a>

and there is a different MAGI calculation for purposes of a Trad IRA deduction. See worksheet 1-1 here:
<a rel="nofollow" target="_blank" href="https://www.irs.gov/publications/p590a#en_US_2018_publink100025076">https://www.irs.gov/publications/p590a#en_US_2018_publink100025076</a>

Thanks, SweetieJean. Your advice helped me to find the MAGI calculation for purposes of a Roth IRA

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Unfortunately I can't paste the link to the comment (I don't know how). Sorry for the testing on the number.

You can find it in the same URL posted by SweetieJean (<a rel="nofollow" target="_blank" href="https://www.irs.gov/publications/p590a#en_US_2018_publink">https://www.irs.gov/publications/p590a#en_US_2018_publink</a>), just search for Worksheet 2-1. Modified Adjusted Gross Income for Roth IRA Purposes

The worksheet 2-1 doesn't include rental loss and here is the inclusion:
1. Enter your adjusted gross income from Form 1040, line 7; or Form 1040NR, line 35 1.
2. Enter any income resulting from the conversion of an IRA (other than a Roth IRA) to a Roth IRA (included on Form 1040, line 4b; or Form 1040NR, line 17b) and a rollover from a qualified retirement plan to a Roth IRA (included on Form 1040, line 4b; or Form 1040NR, line 17b) 2.
3. Subtract line 2 from line 1 3.
4. Enter any traditional IRA deduction from Schedule 1 (Form 1040), line 32; or Form 1040NR, line 32 4.
5. Enter any student loan interest deduction from Schedule 1 (Form 1040), line 33; For Form 1040NR, line 33 5.
6. Enter any domestic production activities deduction (DPAD) from Schedule 1 (Form 1040), line 36, or Form 1040NR, line 34 6.
7. Enter any foreign earned income exclusion and/or housing exclusion from Form 2555, line 45, or Form 2555-EZ, line 18 7.
8. Enter any foreign housing deduction from Form 2555, line 50 8.
9. Enter any excludable qualified savings bond interest from Form 8815, line 14 9.
10. Enter any excluded employer-provided adoption benefits from Form 8839, line 28 10.

Premium Tax Credit form 8962 line 2a says to enter Modified AGI.