# Primer Design ## General Considerations ## Offsite Primers Mutagenesis > See also: > - [QuickChange Primer Design Help](https://www.agilent.com/store/quickchange-primer-design-help.jsp) > - [Oligonucleotide Properties Calculator](http://biotools.nubic.northwestern.edu/OligoCalc.html) - Ideally, the primers have a minimum GC content of 40% and terminate in one or more C or G bases at the 3’ end. - Primers should be between 25-45 bases in length - Tm should be ≥ 75 - If necessary, primers can be longer than 45bp to achieve this, but it does increase the likelihood of