Your tax return will be filed as if you were married for the entire year. To estimate your new correct withholding, you can use the IRS estimator tool here,
https://www.irs.gov/individuals/tax-withholding-estimator
You will input information for both you and your spouse's jobs and other income. You may need to modify one or both of your W-4s. You should also run the estimator again in February, since the changes that are made for the last 3 months of 2020 might not be appropriate for a full year.
