Why fit drifts between appointments
A saddle fitted in spring is fitted to a spring horse. Through a season his topline builds with work or melts away with a spell off, his weight creeps with the grass, and the flocking in the panels settles and compacts with every ride. None of that waits for your fitter's next visit, which is why the fitter's parting advice is usually to watch the fit yourself. Your job is not to re-fit the saddle but to catch the drift early, while it is still a matter for an adjustment rather than a sore back and weeks of lost work.
The static checks, done the same way each time
Stand him square on level ground and girth the saddle up exactly as you ride in it, with no numnah or pad underneath, because pads disguise the very contact you are trying to assess. Run a hand between the pommel and the withers: you are looking for roughly two to three fingers of clear space all the way down the gullet channel, and that channel should stay clear along the whole spine. Slide a flat hand under each panel from front to back; pressure should feel even, with no tight spot pinching at the front and no gap where the panel lifts away mid-back. Sight along his spine from behind to confirm the saddle sits straight, and sit in it or have a rider sit in it to check the seat lies level rather than sliding you toward the pommel or the cantle. Finish by rocking the saddle gently; a well-fitting tree stays put instead of rolling.
The sweat pattern tells the truth
After a proper ride on a warm day, untack and look at his back before you brush it. An even sweat mark matching the shape of the panels is what you want. Dry patches standing out in a sweaty panel outline are pressure points, because pressure shuts down sweat glands; a mark that is dry in the middle and sweaty at front and back suggests the saddle is bridging across his back. Read this evidence with the static checks rather than on its own, since a short or gentle ride will not produce a readable pattern at all.
Behaviour and body changes between rides
Your horse votes on fit every day. Note ear-pinning, tail-swishing or trying to bite when the girth is tightened, a back that dips away when you groom or press along it, reluctance to go forward, hollowing in transitions or a new habit of rushing. On his side, feel for white hairs appearing in the saddle area, for flaky or rubbed patches, and for tender spots that make him flinch. Compare his shape honestly, too: a horse who has gained a topline or dropped weight since the fitter came is standing in a different body under the same saddle.
When to move the fitter's appointment forward
Book the fitter early if the wither clearance shrinks, if your flat hand finds a new pinch or gap, if dry pressure islands appear twice running, or if soreness signs persist across a week of ordinary work. Do not try to correct a slipping or pinching saddle with thicker pads as a long-term answer; padding changes the balance you have just measured and can make a narrow fit worse. A short note of what you found and when is far more useful to the fitter than a general feeling that something is off. Listing the monthly fit check among his KinsLe Care Teams duties, with findings logged each time, gives that note a home and makes sure the checks actually happen between visits.