The impact of Brexit on the FTSE 100 will depend on whether the UK leaves with or without a deal. Since the 2016 referendum, the FTSE 100 has tended to move inversely with the pound. This means that while the pound has tended to rise when it seems likely that a deal will be in place for Brexit, the FTSE 100 has tended to fall. Conversely, the pound has tended to fall when a no-deal Brexit seems more likely, causing the FTSE 100 to rise. That’s because UK-based FTSE 100 constituents earn a lot of their income in other countries, and these earnings are worth more when profits are converted to pounds if sterling’s value has fallen relative to other currencies. Depending on the outcome, the pound may decline further and boost the FTSE 100’s value, or vice versa. Whatever happens, the index’s volatility is likely to continue post-Brexit.