Graphs are one of the few things that spreadsheet programs do well and deservingly so. The already mentioned LibreOffice Calc creates fine spreadsheets and graphs.
OP says free, it's definitely not free.
MS Office is more expensive than my yearly hosting fees.
MS Office is more expensive than Windows.
MS Office is probably the single most expensive piece of software any non-professional person will buy. Not to mention an unneeded expense at that since the free Office offerings are more than good enough for non-professional needs.