I believe you are looking at the one year average annual return [0] which is 27.51% [1].

The Nasdaq-100 is down 22.10% YTD [3].

[0] https://www.investopedia.com/terms/a/aar.asp

[1] https://www.nasdaq.com/market-activity/total-returns

[3] https://www.slickcharts.com/nasdaq100/returns

How are these numbers calculated? It doesn't make sense to me.

There are apparently 2 different indices

NDX: NASDAQ 100 Index

2021-04-27 13960

2021-04-28 13902

2021-04-29 13970

2022-04-28 13456

2022-04-29 12854

https://finance.yahoo.com/quote/%5ENDX/chart

XNDX: NASDAQ-100 Total Return

2021-04-27 16360

2021-04-28 16291

2021-04-29 16372

2022-04-28 15880 (matches your [1])

2022-04-29 15170

https://www.barchart.com/stocks/quotes/$XNDX/interactive-cha...

I can't figure out what the difference is between them.

QQQ is a fund that tracks one of them, but I don't know which. It apparently all 3 match very closely:

https://seekingalpha.com/symbol/XNDX/charting?compare=XNDX,Q...

QQQ's "1-Year Daily Total Return" is -6.78% and its "1-Year" "Trailing Returns" "Monthly Total Returns" is 9.54%. How come those numbers are so different? Shouldn't they be essentially the same?

These other sites say QQQ's "1 Year Return" is -2.78%.

https://www.bloomberg.com/quote/QQQ:US

https://etfdb.com/etf/QQQ/#performance

I don't understand any of these numbers. How can this stuff be so contradictory?

NDX = capitalization-weighted index (i.e. the higher marker cap companies in the index will be a greater % of the index) [1]

XNDX = a total return index tracks the price + reinvests all dividends back in to the index [2]

[1] https://www.investopedia.com/terms/n/nasdaqcompositeindex.as...

[2] https://www.investopedia.com/terms/t/total_return_index.asp

I believe total return includes dividends. So QQQQ's price tracks the index, but your total return for QQQQ (i.e., increases in value plus dividends paid out to you) would track, well, the total returns. Not sure why different sites don't align.

That doesn’t seem to be the case. According to the source below it’s down 7%. What am i missing.

[1] https://www.cnbc.com/quotes/.NDX?qsearchterm=nasdaq

you’re not missing anything. slaw has called this one wrong