The first week lies to you
The log in the form is a real shape: 2.480 down to 2.281 in the first week, then 2.140, then 2.041, then 1.968 at day 28. Those are drops of 0.199, 0.141, 0.099 and 0.073 — each week about seven tenths of the one before. As a share of the green weight, which is the column the page prints, the rate falls from 1.15 percent a day in week one to 0.81, then 0.57, then 0.42 in week four.
That is what a surface drying out does. Early on the water is right there; later it has to move through a rind that is doing its best to stop it. Any projection built on the early rate is built on a number that has already stopped being true.
Three answers that do not agree
At day 28 the piece is at 1.968 and 20.65 percent off its green weight. Suppose the finished weight in the form, 1.612, is what your own formulation calls for. There is 0.356 still to lose, and the three ways of estimating how long that takes give:
The straight line from day zero has been averaging 0.018286 a day, so 20 more days. The straight line from the last week has been doing 0.010429 a day, so 35 more days. The exponential fitted to the last week gives 39 more days. Earliest to latest is a factor of two, and the first of them is the one people actually use.
The right way to read that is not to pick one. It is to notice that the finish is five weeks away rather than three, to weigh it again next week, and to watch the estimates converge as the remaining distance shrinks.
Why the page prints the rate for every interval
A single average hides the shape. Four intervals in a column, each with its own percent-per-day, shows the fall directly, and it also shows the weeks where something went wrong. A rate that suddenly rises is not the meat drying faster — it is almost always the room, the airflow or the scale, and knowing which week it happened in is how you find out what changed.
The other thing a column of intervals catches is a gain. A piece that reads heavier than last week has not absorbed water out of nowhere; something about the weighing changed. Same scale, same hook, same string, same time of day, every time.
What this is not
It is a division. Weight lost over green weight, and a rate over days. It measures nothing, tests nothing and knows nothing about what is going on inside the piece — not the water activity, not the salt distribution, not what is or is not growing in it. It will not tell you that a piece is ready and it will not tell you that a number is enough, because it has no way to know either of those things and because dry curing is the food category where the consequences of a confident wrong answer are worst.
The target weight in the form is yours. Where it came from — a tested formulation, a recipe you trust, somebody qualified who looked at your setup — is the part that matters, and this page has no view on it and offers none.
Questions people ask
How do I calculate weight loss percentage when curing?
Green weight minus current weight, divided by green weight. At the log in the form, 2.480 down to 1.968 is 0.512 lost, which is 20.65 percent. The one thing to get right is that it is always measured against the green weight at hang-up, not against last week — cumulative percentages taken week by week do not add to the total.
Why is my curing taking longer than I calculated?
Almost certainly because you projected from an early rate. Drying slows as the outside dries out: at the default log the rate falls from 1.15 percent of green weight a day in the first week to 0.42 in the fourth. A straight line from day zero puts the finish 20 days out where the last-interval rate puts it 35 days out, and that factor of nearly two is entirely down to which rate you used.
Which of the three projections should I use?
None of them on its own. They are printed together so the disagreement is visible, and the honest reading is that the answer sits somewhere between the last-interval line and the exponential, and moves every time you add a weigh-in. Weigh twice a week and watch them converge rather than picking one and marking a calendar.
What weight loss should I dry to?
This page has no view and will not offer one. The target field asks for the finished weight your own tested formulation or your own guidance specifies for this piece, and everything downstream is arithmetic on that number. Weight loss is a division, not a test, and nothing here measures water activity or anything else about what is going on inside the meat.
My piece gained weight between weigh-ins. What does that mean?
Not that it absorbed water. It means something about the weighing changed — a different scale, a wet hook, extra string, a piece that picked up condensation, or a reading taken at a different point in the day. The page reports the gain and draws no conclusion, because the useful response is to fix the measurement rather than to interpret it.