I don't know why this year i have to fill out form 2210. Every year we owe money, but his year 2018 we need to complete this form and i don't understand why.

[MichaelMc]

Many taxpayers are finding that their refunds are smaller than expected or that they owe taxes this year.

In 2018, the withholding tables used by employers were adjusted to put more money into wage earners' paychecks. This was done without fully taking into account the impact of many tax law changes that were also taking effect in 2018. The consequence is that many taxpayers are seriously under-withheld.

Form 2210 is completed to calculate your penalty for being under-withheld. You probably still need to complete it but please see the following notice regarding special relief granted by the IRS for 2018 only.

Per the IRS:  "The IRS is generally waiving the penalty for any taxpayer who paid at least 85 percent of their total tax liability during the year through federal income tax withholding, quarterly estimated tax payments or a combination of the two. The usual percentage threshold is 90 percent to avoid a penalty."  https://www.irs.gov/newsroom/irs-waives-penalty-for-many-whose-tax-withholding-and-estimated-tax-pay...