Turnover increased by £1.4m to £6m, driven by increased gate receipts and sponsorship plus record merchandise and bar sales.
That saw Castleford - on the brink of going bust in 2013 - generate a profit of £691,000, their biggest yet and the fourth successive year of finishing in the black.
It allowed them to increase their salary cap spend for this season and Fulton said: “This club is now in such a healthy place financially.
“The extra investment in the players’ budget is really bearing fruit for us right now, especially with so many injuries to key players.
“For us to be in the top-four and challenging for the 2018 Betfred Super League Grand Final is just fantastic.”
Meanwhile, Leeds Rhinos’ Stevie Ward has been cautioned for a dangerous contact on Hull KR’s Justin Carney during Saturday’s Qualifiers defeat but has not received any suspension.
Also, the RFL have appointed two more full-time match officials.
Referees Gregory Dolan, from Batley, and Thomas Grant, from Leeds, have both been promoted by RFL match officials director Steve Ganson.
Elsewhere, Catalans Dragons forward Louis Anderson, 33, has confirmed he will retire at the end of the season.
The former New Zealand star has been in Perpignan for seven years having also enjoyed success with Warrington Wolves.
Catalans coach Steve McNamara said: “His decision to retire after a glittering career will leave a big void to fill within our team.”