Question: "Should a Christian tithe off miscellaneous income, e.g. inheritance, gifts, winnings, tax refunds, legal settlements, etc.?"
For an general understanding of the issue of tithing for Christians, please see https://www.gotquestions.org/tithing-Christian.html.
Answer: Whether or not a Christian should give a percentage of an inheritance—or for that matter any source of income—to the church or other Christian ministry is the subject of debate within the Christian community. There is also the question of whether or not an inheritance can even be considered income. As for the amount of our giving, some in the Christian church have taken the 10 percent figure from the Old Testament tithe and applied it as a “recommended minimum” for Christians in their giving. Some say give on what you make before taxes (gross income), and others say give on what is left over after taxes and deductions (net income). Much debate and argument on the details of tithing and giving have needlessly occurred, sometimes even splitting churches and dividing Christians from one another.
It should be remembered that the tithe was a requirement of the Mosaic Law in which all Israelites were to give 10 percent of everything they earned and grew to the Tabernacle/Temple (Leviticus 27:30; Numbers 18:26; Deuteronomy 14:24; 2 Chronicles 31:5). In fact, the Old Testament Law required multiple tithes which would have pushed the total to around 23.3 percent, not the 10 percent which is generally considered the tithe amount today. But the Bible is clear that tithing was part of the Mosaic Law for the nation of Israel, not for all mankind. Just as Christians are not required to sacrifice animals or observe the ceremonial laws regarding washing and other rituals, neither are we required to give a set percentage of our income, regardless of how it is acquired.
The New Testament references giving in 1 Corinthians 16:1-2, and there we find the principle for giving for Christians. Paul exhorts the Corinthian church to set money aside “for God’s people,” to do it on the first day of the week, and to save it and set it aside in keeping with the income of the giver. “Income” is not defined, except that in the King James Version, the word is translated “as God has prospered him.” From this we can say that inheritance, gifts, winnings, tax refunds, legal settlements, etc., are part of being prospered by God and should be included in income. But, again, the amount of the inheritance to be offered is not defined. Another principle for offerings is found in 2 Corinthians 9:6-7 where Paul again exhorts the Corinthian believers to give generously from their hearts, each one deciding before God what to give. Paul explains that it is not the amount or the percentage or the source of the income, but the attitude of the heart that is important to God. Each should give “cheerfully,” not as one under the compulsion of a legalistic mindset or the requirements set down by others. We should never give to get, never give to be noticed, and never give to be spiritually rewarded. If we are in fellowship with God and at peace with our giving, then all is well. As with all things, wisdom should be sought from God, who has promised to give it generously (James 1:5), just as we are to generously and cheerfully give back to Him.