~ quarterly
   (a)   $1

;~ every 15th day of month
;   (b)   $10

2020-01-01 regular transaction
   (a)   $1

comment

~/src/hledger/examples$ date
Thu Dec 10 14:29:49 PST 2020
~/src/hledger/examples$ hledger -f forecast.journal print --forecast
2020-01-01 regular transaction
    (a)              $1

2020-04-01
    ; generated-transaction: ~ quarterly
    (a)              $1

2020-07-01
    ; generated-transaction: ~ quarterly
    (a)              $1

2020-10-01
    ; generated-transaction: ~ quarterly
    (a)              $1

2021-01-01
    ; generated-transaction: ~ quarterly
    (a)              $1

2021-04-01
    ; generated-transaction: ~ quarterly
    (a)              $1