Upgrading calculations

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The base cost for upgrades is 1/2 and the base time is 1/4

There are two parameters for upgrading: one in \db\misc.txt and the other for each unit or bde in your \db\units files which is almost uniformly the same unless modified. This typically looks like:

upgrade_time_factor = 0.5
upgrade_cost_factor = 1.0

From misc.txt:

# Upgrade cost 
0.5
# Upgrade time
0.5

Then calculate the upgrade percentages from the standing/drafted army slider and the free_trade/central_planning slider. These sliders determine Gearing Bonus, in addition to upgrade time. Use decimal format rather than percentages (85% means .85)

Multiply the .5 * (1+upgrade) for cost
Multiply the .25 * (1+upgrade) for time

So if your upgrade total was .8,

cost would be .5 * 1.8 * IC cost for the new model
time would be .25 * 1.8 * time needed for the new model

Upgrades can be done for land and air units and most brigades. Naval units can not be upgraded.

EXAMPLE

Soviet Union upgrades 1936 mountain div to 1939 mountain div. SU has 90% upgrade from army slider and 25% upgrade from the economy slider netting 115%. New 1939 mountain div costs 6.4 IC for 96 days (upgrades are based upon your current model and all minister, slider, and tech effects apply to the upgrade cost and time).

Cost = 6.4 * .5 * (1+1.15) = 6.88
Time = 96 * .25 * (1+1.15) = 51.6 days

Cost comparisons: Total cost for new units and for upgrading is IC cost per day * total numbers of days. Ignoring the rounding factor for days (51.6 would mean 52 days), the comparative costs are:

New model = 6.4 * 96 = 614.4 IC days
Upgrading = 6.88 * 51.6 = 355.008 IC costs
Comparative upgrade percentage = 355.008/614.4 = 57.78%

Basically the percentages you see on the diplomatic screen slider section are higher than the actual calculated upgrade cost. Upgrades are not as expensive as they seem until you do the math. Note that the army slider upgrade percentages are cut in half in Doomsday which ranges from 5% to 50% while in HOI2 the upgrade percentages range from 10% to 100%.

Table comparing displayed with actual upgrade cost %

Here is a table of the actual upgrading costs for the displayed upgrading percentages:

display % cost
125	63.28%
115	57.78%
105	52.53%
95	47.53%
85	42.78%
80	40.50%
75	38.28%
70	36.13%
65	34.03%
60	32.00%
55	30.03%
50	28.13%
45	26.28%
40	24.50%
35	22.78%
30	21.13%

Upgrading Twice Obsolete Models

In version 1.3, upgrading twice obsolete models is very fast due to a second 1/4 time reduction. By twice obsolete, that means first finishing the research on model 3 and then upgrading model 1 to model 2. It takes only around 14 days to upgrade Int-1 to Int-2 if you already have Basic Interceptors (Int-3) researched. It takes only around 18 days to upgrade Tac-1 to Tac-2 if you have Basic Tactical Bombers (Tac-3) already researched.

More details can be found in this thread.

Upgrading an old serial run vs starting a new run

The math for this is complicated. Slider positions influence this somewhat, but gearing is more important than your slider positions. Generally it can be cheaper if you keep an old run going if you do not build much of a new run. More details can be found in this thread and or a thread which shows the math."

General rules of thumb contrasting keeping an old serial run going vs starting a new serial run with a new model:

1) By the 5th or 6th new model, the new model is cheaper than keeping the old run going with it's production + upgrade costs. This is primarily due to gearing costs equalizing.

2) If you consider the average cost, however, it takes until the 9th or 10th production of the new model to be better on average than continuing the old model.

3) If the production costs of the old model are cheaper than the new model [ex. armor or bombers], it is even more advantageous to continue the old model.

4) Slider positions do NOT influence this a lot compared with gearing. Gearing is more important, which is why continuing an old model that has lots of gearing is usually preferable.

Light armor exception

There is one exception to the general rules on upgrading: light armor divisions. Light armor crosses model category since light armor upgrades to armor. Due to this crossover, light armor upgrades have 2 rather than 1 full time and cost upgrades: first to the improved light armor division model and then another full time and cost upgrade to armor [basic medium armor III]. If you want to build up armor with a long serial run, do this with armor-II, not with light armor such as the tankette.