Swap points are calculated taking into account interest rates difference, and basis.
Basis is just the liquidity preference in one currency against the other, and is subjective, not being possible to calculate it from a formula or anything know.
Let’s say “basis” is the part of swap points that differ from interest rates diferencials, and as I told you before, it is explained by liquidity preference in one currency against the other.
In EURUSD, because of year end and preference in funding in USD to match balances, swap points for overnight hit 22 basis points (0,0022), situation that became normal in jan 2017.
That’s why you have seen such big changes in swaps these days.