How do I know if I'm being underpaid?

Start with three external reference points. Glassdoor + LinkedIn salary insights for your specific role and city is the broad reference. Recruiter outreach with named salary ranges (genuine outreach for the role you do) is the more reliable one — recruiters quote actual market bands. Former colleagues at similar level and tenure who'll tell you their numbers honestly is the third. Two of three pointing the same direction is reliable.

The 15% rule. Across UK roles I've placed, candidates whose current salary is 15%+ below median for their specific role and city consistently exit within 18 months. Smaller gaps (5-10%) tend to resolve at next review or annual cycle; bigger gaps (15%+) almost never resolve internally and require external moves to correct.

What internal moves typically achieve. UK internal promotion shifts run 8-15% on average. External moves at the same level shift 20-30%. So if you're 15%+ below market, an internal pay rise probably won't close the gap — you need to interview externally. The threat of leaving often unlocks more than the asking does.

The conversation worth having first. Before assuming you're underpaid, talk to your manager about your specific position in the band. Some managers don't know themselves; many will check and come back with the answer. If you're at the bottom of the band for your level, that's a fixable conversation. If you're already at the top of band, the conversation has to be about getting to the next level, not the next pay rise.