FROM THEN ON / SINCE THEN
The time expression “from then on” occurs very frequently with the past tense, because the span it covers falls completely in the past.
She had a car accident at 13. From then on she had to be in a wheelchair. Life became challenging but she was still upbeat.
If a span extends from a point in the past to the very present moment, we normally use “since then”, rather than “from then on”.
I joined the staff when I was graduated from college. Since then I have been teaching here.
It would be awkward to say:
I joined the staff when I was graduated from college. From then on, I have been teaching here.
Is it possible to use “from then on” for the future? Definitely.
After she gets her degree, she will find a job in an American company. From then on she will be an American citizen.
Shengliver Studio 