Using mail merge in excel without word

if there is a field in each sheet that has the exact same unique value like employee number or full name, you can use the Excel function VLOOKUP to add data into a cell in one sheet from another row in another sheet

Ah!  Two sheets with entirely dissimilar structures.  That's what I suspected, which is why I asked the question.

So my answer would be: "I wouldn't merge them!" The main reason being that the Time and Wages sheet presumably contains complex calculation logic that you do not want replicated into multiple instances (because if you do, you will get a maintenance nightmare when anything in the rules changes). You would have to track down, and update, every single worksheet.

What I would do is "link" the two sheets, so that one is simply drawing data from the other.

Whether you link from Time Sheet to Pay Sheet, or from Pay Sheet to Time Sheet depends on which person you expect to do the most updating.

If you want each employee to fill in their own timesheet, and the Pay Lady (it's always a lady, men don't have the patenince to do this properly...) to calculate the wages, I would link from the Pay Sheet to the Time Sheet.  So you place a set of 31 rows on the timesheet containing each day of the month, with columns for start time, break time, finish time, leave type etc.

Then you put a row for each employee in the Pay Sheet, which draws the data from each employee's time sheet and computes their wages.

Some design considerations:  When you retrieve the employee's time, you MUST also bring across the DATES.  And you should time-stamp the data with the date and time that you retrieved it. Then you need to make provision to store the raw data for up to seven years (in Australia you have to keep financial data that affects the employee's tax position for up to seven years; I do not know which jurisdiction you are in, or what your retention requirements are, but there will be some!)

You will need to import the data into "Helper Columns" (which can be hidden) so that you can implement "Closing" logic to the data import (If the entry is for a date prior to last Thursday, and I already have data in this row, then do not import again...) to prevent the employee going back and "adjusting" last week's attendance. You need to keep accrual totals for things such as leave and sick day entitlement and decrement them.

Excel is not the tool to use to do this job! The logic becomes very complex, the spreadsheet will become very slow if there are a lot of employees, and the impact to the business from a logic error is potentially catastrophic.

I would keep the employee Time Sheet in Excel, perhaps; but rely on a proper accounting back-end such as MYOB (https://www.myob.com) to do the calculation and store the data. Applications like that have decades of development and refinement: the chances of getting a catastrophic risk from a logic error is infinitesimal -- and they're easier to use than Excel for this purpose.

Hope this helps