Common Types of Data Issues in Excel

In practice, problems in data are usually repetitive. You will often see the same types of mistakes again and again, especially when working with imported or manually entered data.

One of the most common issues is when numbers are stored as text. Visually, they look like normal numbers, but Excel does not treat them as numeric values. Because of this, formulas like SUM or AVERAGE may ignore them or return incorrect results.

Another frequent problem is inconsistent date formats. In one column, you might see dates written as 01/02/2024, 2024-02-01, or even Feb 1 2024. Excel may interpret some of them correctly and others as text, which breaks sorting and filtering.

Let's look at a simple example:

At first glance, the table looks fine, but several issues are hidden inside.

The value "20" is stored as text instead of a number. The dates are written in different formats, which may prevent correct sorting. Also, the same product appears multiple times, which may or may not be intentional, but needs to be checked during analysis.

Most Excel problems come from a small set of repeated issues. If you can quickly recognize them, you will save a lot of time during data cleaning.