How to make Less indicate location in percentage

export LESS="-m"

More generally, the LESS environment variable may contain options equivalent to command line flags you could explicitly pass when running less -- here, the -m option that tells it to prompt more richly (including the percentage, as you asked). You could pass also more than one option within that single environment variable by ending each with a $. For much more info, see less's manpage.

Edit: it is of course possible (depending on how you're using less, e.g. if you're piping to it rather than calling it on a file) that less doesn't know the total size it will be displaying, in which case of course it can't show the % -- in that case it will prompt with what little info it does have, e.g., how much text has it shown so far. For example, man does use less that way, by piping.

So, if your specific need is to see the % in man (rather than when calling less directly on a file) you need to use an "alternate pager" (environment variable MANPAGER or switch -P on the man command line) which is a simple script that saves man's output to a temp file and then uses less on the latter. (That may lose man's own "colorization" unless you play yet further and deeper tricks, etc, etc -- similarly you might use the "preformat pages" option of man and uncompress such a preformatted page to a tempfile on which to run less, etc, but this is starting to become a somewhat complex "simple script";-).

Solution

A less manual version of knitatoms' answer combined with Alex Marteilli's answer works quite well: pass the +Gg option to less via its pager option.

For example, try

man -P 'less -s -M +Gg' man

This can be effected permanently by putting

export MANPAGER='less -s -M +Gg'

in one of your shell configuration files (above syntax is for Bash and ZSH). Now, for example, man man displays the percentage as you wanted!

Warning

You should not put the +Gg in the LESS variable! For example, doing

export LESS='-M +Gg'

will cause problems when reading very large files. For example,

yes | LESS='-M +Gg' less

does not work very well ...

Explanation

As other answers have explained, the problem is that less can't say what percent into the file you are until it knows how long the file is, and it doesn't read to the end of the file by default when reading from a pipe.

From the OPTIONS section of man less:

+      If  a command line option begins with +, the remainder of that
       option is taken to be an initial command to less.   For  exam‐
       ple, +G tells less to start at the end of the file rather than
       the beginning, and +/xyz tells it to start at the first occur‐
       rence of "xyz" in the file.  As a special case, +<number> acts
       like +<number>g; that is, it starts the display at the  speci‐
       fied  line  number (however, see the caveat under the "g" com‐
       mand above).  If the option starts with ++, the  initial  com‐
       mand  applies  to  every file being viewed, not just the first
       one.  The + command described previously may also be  used  to
       set (or change) an initial command for every file.

The g means "return to the beginning of file".

The -M tells less to show a "long prompt", which in particular includes the percentage. But it seems man makes less include the percentage automatically, even if you leave -M out, if man detects a "recent version of less". See the -r prompt section of man man for more info.

From the man man (in 2013):

-P pager, --pager=pager
       Specify which output pager to use.  By default, man uses pager
       -s.  This option overrides the $MANPAGER environment variable,
       which in turn overrides the $PAGER environment  variable.   It
       is not used in conjunction with -f or -k.

       The value may be a simple command name or a command with argu‐
       ments, and may use shell quoting (backslashes, single  quotes,
       or  double  quotes).  It may not use pipes to connect multiple
       commands; if you need that, use a wrapper  script,  which  may
       take  the file to display either as an argument or on standard
       input.

Note that it says -s is the default option used with the pager by man. In 2022 I no longer see the -s mentioned here in man man, but I don't see any harm in leaving it in (it squashes consecutive blank lines).