How to use the online timer
Three minutes is the standard for a builder's brew: water at a full boil poured straight onto the bag or leaves, then left alone. Most everyday black tea gives its flavour in the first two minutes and its tannin in the third and fourth, which is why a bag forgotten for six minutes tastes harsh and drying rather than simply stronger. Anywhere between three and four minutes suits most people, and it is worth finding your own number rather than guessing each time.
Boiling water matters more than the brand. Water that has gone off the boil sitting in the kettle, or reboiled several times, gives a flat cup, and warming the pot first keeps the temperature up through the brew. Green and white teas want the opposite treatment entirely: cooler water, around 80°C, and a shorter steep, or they turn bitter within a minute.
When the time is up, take the bag out rather than leaving it in the mug to keep going, and resist squeezing it against the side, which pushes out exactly the bitter compounds you have just avoided. For a stronger cup, use more tea rather than more time. Milk goes in whenever your household has always put it in; the argument predates the timer and will outlast it.
Common questions
Does brewing longer make tea stronger?
Only up to a point. Most of the flavour comes out in the first two or three minutes and mainly tannin follows, so a longer steep tastes bitter rather than stronger. Use more tea instead.
Does reboiled water really matter?
It gives a flatter cup, since repeated boiling drives off dissolved air. Fresh water brought to a proper boil, poured straight onto the tea, makes a noticeable difference.