Anyone knows how StashAway time-weighted return and money-weighted return are calculated?

Hi there! Time-weighted returns do not take into account the effect of an individual’s contributions or withdrawals. Now why does deposit or withdrawals matter? Because if an investor contributes a significant sum into their portfolio just prior to the portfolio’s performance rising, intuitively, this is a positive action. But if the investor withdraws a significant sum from their portfolio just prior to the portfolio’s performance rising, intuitively, this is a negative action.

Money-weighted returns take into account of when you put the money in. So it measures whether you timed the market correctly.

But since you use stashaway, it doesn't really matter which one you look because it is hard to time the market. If you really want to reduce the impact of timing the market, you can do Dollar Cost Averaging.