How much should a person donate to church?

The answer is simple—as much as God leads you to give. However, know that followers of Christ view the tithe as a baseline for giving—a starting, not an ending point.

Christians draw on the following Scriptures and principles to conclude that giving is a kind of litmus test for spiritual maturity and that "God loves a cheerful giver" (2 Corinthians 9:7).

•       In Old Testament times, God's people were to give a tithe (a tenth of their gross income). That offering was an expression of gratitude to God—for all He has done, was doing, and would do in the future. Followers of Christ believe the tithe principle still applies to people of faith today (2 Corinthians 9:12).
•       In Old Testament times, God's people were also expected to give 20% of their income to support various civic, government, and religious projects. In addition, God called His people to give special offerings (for example, Temple projects) and seasonal offerings in conjunction with the Festivals. Followers of Christ believe that generous giving is pleasing to God and that generosity is marked by giving beyond the tithe.
•       Believers in the Old and New Testament did not receive charitable gift donation slips for tax-use purposes—they gave because they believed God expected them to give. Christians in many nations today can receive a tax benefit when they give to a church or non-profit organization. However, the motivation to give should be to be faithful to God,  not  to receive a financial benefit.
•       Matthew 10:42 notes how no act of charity goes unseen by God or unrewarded.
•       In John 6, we see that when we give, God blesses.
•       The Apostle Paul wrote, "Whatever you do, do it all for the glory of God" (1 Corinthians 10:31). Christians believe that the verse applies to how we live and give. Some link this verse to the God first teaching, meaning believers are to support God's work by giving the first and best part of all they have (1 Corinthians 16:2; Malachi 3:8-10; Proverbs 3:9-10).
•       Christians believe that God owns everything—we are simply the stewards of His resources. This mindset makes it easier to give as God desires (1 Chronicles 29:14-18; Psalm 50:10-12).
•       Christians believe Scripture advocates investing in the future by giving generously today (Matthew 6:19-21).Christians believe that giving today merits a reward in heaven tomorrow (1 Timothy 6:18-19).

How much can I deduct for church donations?

Tax laws vary from country to country. In the United States, the IRS allows a tax deduction of up to 50% of one's salary or gross income for charitable donations to a church. Note: This includes financial gifts and donations of items and services.

Summary: 

Scripture teaches that we will reap what we sow (2 Corinthians 9:6). Those who are generous model the example of God and Christ. Scripture notes that we are to "Receive in God's name and give it away generously in His name" (Acts 2:44-47). The encouragement, then, is to generously support worthy causes, beginning with God's gift to this age, the Church. Those who give will be blessed.