what formula can be used to have extra deposit of 25 dollars every 3 months or 2 months?

Savings Account Calculator Results Enter Values Starting Balance $ Scheduled Deposit $ Annual Interest Rate Extra deposit every how many month(s) How much extra to deposit $ Start Date of Account Goal $ 1,000.00 25.00 1.25% 3 25.00 919 2,000.00 total number of deposits needed total number of extra deposits total amount of extra deposits total amount of interest earned how long to achieve goal (months) DepNo. 1 2 3 4 5 6 Beginning Deposit Date Balance 9/19/2020 1,000.00 $ 10/19/2020 $ 1,026.07 $ 11/19/2020 $ 1,052.16 $ 12/19/2020 $ 1,078.28 $ 1/19/2021 $ 1,104.43 $ 2/19/2021 $ 1,130.61 $ 3/19/2021 $ 1,156.81 $ 100 Deposit 25.00 $ 25.00 $ 25.00 $ 25.00 $ 25.00 $ 25.00 $ 25.00 $ Interest Extra Deposit Total Deposit 1.07 $ 26.07 $ 1.09 $ 26.09 $ 1.15 $ 25.00 $ 51.15 $ 1.15 26.15 $ 1.18 26.18 $ 1.20 26.20 $ 1.23 26.23 $ 1 on Amount Left to Ending Balance Reach Goal 1.026.07 $ 973.93 1,052.16 $ 947.84 1,078.28 $ 921.72 1,104.43 $ 895.57 1,130.61 $ 869.39 1,156.81 $ 843.19 1,183.05 $ 816.95