Why do I have a negative time-weighted return, but positive dollar return?

Your TWR is negative because your portfolio’s return has decreased in value since your first deposit.

Here’s an example of when this might be the case:

Let’s say you deposited 100,000 THB to start your StashAway account in January and the market goes down 10% by September. You’ve lost 10,000 THB (out of 100,000 THB invested) in your portfolio and you’re down to 90,000 THB. You then have an unexpected windfall (lucky you!) and decide to make a 1,000,000 THB deposit in September. By December, the market goes up 5% after the second tranche of investment.

What are my returns like now? Well, you would have positive dollar gains because you just gained about 44,500 THB on a total of 1,100,000 THB invested.

But this wasn’t because the portfolio has performed exceptionally thus far: it went down 10% then up just 5%. However, most of your money was invested right before markets went up.

The time-weighted return is negative because the first deposit of the investment performed poorly between January and December, but your simple dollar return is still positive because of when you made your deposits.