How to calculate how much of dividends will be earned for an ETF?

Published dividend yield is calculated based on the current unit/share price and most recent annualized distribution. Your yield will change over time as you receive dividends.

Assuming you paid the current price of $41.68 per unit for your 100 units of SPYD, your cost basis is $4,168. If the distribution holds to the most recent paid of $0.6362/unit your annual distribution will be $2.5448/share or $254.48 for a yield of 6.1%.

If, next year the unit price is $61, and the quarterly dividend is up to $0.85/unit, the published yield will be something like 5.6% ($0.85 * 4 / $61); but your yield will be based on your purchase price of $41.68, so $0.85/unit would be 8.2%.

Distributions tend to fluctuate over time. The actual most recent annual distributions sum to $1.9026

03/24/2021     $0.6362
12/23/3030     $0.6066
09/23/2020     $0.2636
06/24/2020     $0.3962

If you had bought in June 2020, the unit price was around $28.50; the published yield at the time would have been something like 5.6% ($0.3962 * 4 / $28.50). In the last year you would have actually received $190.26 for your 100 units which cost you $2,850 for an actual annual yield of 6.6%