There is no one "right" answer to this question. It depends. Check registers are very compact and some people like to keep them for historical purposes as a record of their previous income and expenses. There is nothing wrong with this. You could save 20 to 50 years worth of check registers and take up very little space.
Technically, though, check registers only need to be kept for several months for the purpose of balancing your checkbook. How long you keep them beyond that is up to you. Some people recommend keeping checkbook registers for at least 12 months in case "issues" (questions about payment) arise and because some checks may take a while to clear.
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