How to make cell's data entry always negative numbers without having to enter the minus sign.

You can prevent entering of positive numbers in the first place by setting up Data Validation on the whole (or desired part of the) sheet. Something like this:

Br,

Hi,

Assuming only positive numbers have been entered in range A2:A10, type -1 in cell C1. Copy cell C1, select range A2:A10 and right click > Paste special > Multiply > OK. Hope this helps.

It's not simple

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#1 You can use a custom format to display a minus sign, with the understanding that the value is actually positive when you use it elsewhere

1. Select the entire column you want it to be negative, by clicking on the column header.
2. MAC users Hold down Command key and click in any cell(with selection), WINDOWS users right-click, then click Format cells in the context menu.
3. Click Number tab, click Custom Option, on right-hand side, under Type text box select General, and in the Type text box, enter a minus sign like this: -General and click OK.
   

OR

_(* #,##0,_);[Red]_(* (#,##0,);_(* "-"_);_(@_)

Excel Custom Number Format Guide

https://www.myonlinetraininghub.com/excel-custom-number-format-guide

I’ve put together this Excel custom number format guide as a resource for our members. There are loads of ways to apply custom number formats and as a result I find myself answering questions that are covered in this post on a daily basis.

To be clear, number formatting in Excel is used to specify how a value should appear in a cell or chart, but it doesn’t alter the underlying value that you can see in the formula bar. Unless of course you format a number as text, in which case it can no longer be treated as a number in math formulas.

#2 Use a Helper Column

1. Set one column for data entry of positive value
2. Set another column for negative values(this column/cell only have the ABS formula as follows)
3. IF E1 must have negative value, then choose any column/cell of choice, let's say D1
4. In E1 type =-ABS(D1)
5. Now, whatever value you type in cell D1, the same value will be negative in cell E1
6. Copy the formula you typed once to all cell ranges for example from E1 to E50
7. After finishing all, you can hide the D column which contains D1 positive value.

#3 By Worksheet_Change Macro

This earlier question has a couple of macros you can use https://www.mrexcel.com/board/threads/cell-format-always-negative.53229/

One way is to use data validation to prevent the entry of a number greater than zero.