This is really up to you. Some people want a new one every month or two as an aid to keep their diet on track or further optimise it each month. Lots of myLevels customers have asked for a new sensor after 6 months as they started to get curious about new foods they've started eating. Some people felt they learnt enough the first time so that's all they need. So it's really up to you - try the first one and then see when you get another urge. We'd recommend though for everyone at least once a year as your microbiome (your bacteria in your gut) changes over time and with new situations so your responses could be different a year later.