[Nick]

I have sought the answer in both the TSP website as well as FINRED website. I actually called TSP customer support twice and the two employees I spoke to me they could not answer this question.

What do TSP fund performance percentages actually mean? For example, in 2021 TSP reports the C fund growing by 15.63%, however if you look through each month you don’t see numbers that indicate that’s the average growth for the year. For this I am led to believe that the percentage represents an accumulation of each month’s growth (or decline). But, when I add them all up I get a different number. For C Fund 2021 I am seeing 26.02% when I add each month up, whereas TSP is reporting the fund growth as 28.68%.

Am I missing something? Does my question make sense?

[Sean]

Yeah, you’re missing that is the compound growth rate. If something starts at $100 and gains 10% year one and 10% year two, it “should” be worth $120. Except that’s not correct.

After year 1 it grew 10% to 110. Then year two it grows 10% which is $11 to $121.

[Kirill]

I’m not 100% on the differences you’re seeing/ what motivated you to check the math on this reporting – but it sounds like you could be missing out on some compounding effects if you’re only looking at month-to-month balances.

[Author]

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