John Gill Commentary Leviticus 25:8

"And thou shalt number seven sabbaths of years unto thee, seven times seven years; and there shall be unto thee the days of seven sabbaths of years, even forty and nine years." — Leviticus 25:8 (ASV)

And thou shalt number seven sabbaths of years unto thee
Or weeks of years; and there being seven days in a week, and a day being put for a year, seven weeks of years made forty nine years; the Targums of Onkelos and Jonathan, and Jarchi, interpret it seven "shemittas", or sabbatical years; and a sabbatical year being every seventh year, made the same number;

seven times seven years :
or forty nine years, as follows;

and the space of the seven sabbaths of years shall be forty and nine
years ;
just such a space of years there was between each jubilee, which, as afterwards said, was the fiftieth year; so as there were a seventh day sabbath, and a fiftieth day sabbath, the day of Pentecost, so there were a seventh year sabbath, or sabbatical year, and a fiftieth year sabbath.