Your vaccines give most people around 6 months of relative immunity to Covid-19 variants including Delta and Delta plus

However, let's say you got your shots in February 2021. If you count 5 or 6 months from that date of the last shot you likely should get your booster for whatever shot you got: Pfizer, Moderna, J n J or whatever around 5 months after you got your last shot.

For example, most people I know including me got their shots in March or April. So, you should count about 5 months after March or April before you get your booster to make sure you don't get covid during the winter. IF the next winter is anything like the 1918 Spanish Flu that killed more U.S. soldiers than World War I then the Covid-19 outbreak next winter should be about 1/2 as bad as it was this last winter.

So, you want to get your booster maybe around 5 months after your last vaccination to carry you through the winter months safely.