Other critical factors that are just as important and need to be taken into consideration when making those calculations are PH, water temperature, and how much food is getting tossed into the pond every day. Even if the fish don't eat all the food it won't take long for that food to start getting converted to ammonia. This is why it is recommended that if you start detecting high ammonia levels that you immediately stop feeding your fish. Also the warmer the water is the more adverse effect the ammonia levels will have on the fish. Same goes for PH. "A useful rule of thumb is that at a pH of 8 ammonia is 10 times more toxic that at a pH of 7, and at 68 degrees Fahrenheit it is five times more toxic than at 32 degrees Fahrenheit." However, regarding PH the same sort of situation occurs with PH levels lower then 7.
You can have a pond that seems to be doing fine in cool weather, but if the pond water starts to warm up and the fish start getting active and you start feeding your fish a lot more food, things can go South pretty fast if you don't have the circulation and bio-filtration in place to handle it. This is especially true if your PH levels happen to be very high or low.
I don't know how many times I've seen people (usually kids) kill their aquarium fish simply by over feeding the fish, even though they had previously been doing fine.
For my pond, and probably for most ponds, the most critical time is early spring just as the ice is melting. The critical factors are; lower then normal PH in the spring, the water temperature is warming fast, the bioconversion (as Meyers likes to call it) is low, there is usually an excess of dead plant mater in the pond that is starts decomposing as the water warms which starts producing it's own ammonia, and the fish's immunity is weak. Now add to that the possibility that some over zealous fish keepers may notice their fish being more active and immediately start feeding their fish at mid summer feeding rations, and you end up with a recipe for disaster.