How to make money as the Empire

The Empire's fastest-paying building in Total War: Warhammer III is the Gem Mine (Gem Mining, level 2): 1,000 gold for +400 gold a turn, its cost back in 2.5 turns once built. The most gold from one building slot is the Gemcutter's Workshop at +600 a turn (3,500 gold to build the chain that far, back in 5.8 turns). 54 The Empire building levels make flat income, patch 9.0.4.

Fastest payback

Turns of income to earn the building's cost back (each chain's fastest level).

1Gem MineGem Mining 2 · 1,000 gold → +400 a turn · Region with the resource2.5turns
2Gold MineGold Mining 2 · 1,000 gold → +400 a turn · Region with the resource2.5turns
3Weaving HouseIndustry 1 · 1,000 gold → +250 a turn · Any settlement4turns
4Animal StoreTusks 1 · 500 gold → +100 a turn · Region with the resource5turns
5Brine Mining PitSaltmaking 1 · 500 gold → +100 a turn · Region with the resource5turns
6Cinnabar Mining PitDye Production 1 · 500 gold → +100 a turn · Region with the resource5turns

Most gold per building slot

Income of each chain's top level; the line shows that level's own cost.

1Gemcutter's WorkshopGem Mining 3 · 2,000 gold → +600 a turn · Region with the resource+600a turn
2Gold SmelterGold Mining 3 · 2,000 gold → +600 a turn · Region with the resource+600a turn
3Tailors' GuildIndustry 3 · 2,500 gold → +500 a turn · Any settlement+500a turn
4Estalian Trading PortPort 3 · 4,000 gold → +500 a turn · Port settlement+500a turn
5Imperial PortPort 3 · 6,000 gold → +500 a turn · Port settlement+500a turn
6Alchemy WorkshopMedicine Production 3 · 2,000 gold → +200 a turn · Region with the resource+200a turn

COMPUTEDIncome = the level's flat gold per turn (the game's “Income generated” effects on the building itself, table building_effects_junction) minus its upkeep (building_levels.upkeep_cost). Payback = cost (create_cost) ÷ income. Upgrade payback = the level's cost ÷ the income it adds over the level below. “Gold back by turn” = build turns (create_time) + payback, counted from the order. Chain total = every level's cost up to this one, and its payback = that total ÷ income. Patch 9.0.4.

ASSUMPTIONS

Base values: technologies, lord skills, commandments, campaign difficulty and faction effects that change income or building costs are not counted.
Percentage boosts (“+4% income from all buildings in the province”, “+20% (local region)”) are not in the payback: they depend on the buildings they boost. They are listed below with the income those buildings need to make.
Conditional income (“When Control is 75 or more”, “When enemy Lord is present”…) is not counted; listed below in the game's words.
Resource buildings need a region with that resource; ports need a port settlement. A slot can hold one building, so late in a campaign gold per slot matters more than payback.

Every The Empire building that makes gold (54)

#
1	Gem Mineshaft	Gem Mining	1	500	2	200	2.50	—	4.50	Region with the resource
2	Gem Mine	Gem Mining	2	1,000	3	400	2.50	5	5.50	Region with the resource
3	Gold Mining Pit	Gold Mining	1	500	2	200	2.50	—	4.50	Region with the resource
4	Gold Mine	Gold Mining	2	1,000	3	400	2.50	5	5.50	Region with the resource
5	Gemcutter's Workshop	Gem Mining	3	2,000	4	600	3.30	10	7.30	Region with the resource
6	Gold Smelter	Gold Mining	3	2,000	4	600	3.30	10	7.30	Region with the resource
7	Weaving House	Industry	1	1,000	1	250	4	—	5	Any settlement
8	Clothier	Industry	2	1,750	2	375	4.70	14	6.70	Any settlement
9	Exotic Animal Tamer	Exotic Animals	1	500	1	100	5	—	6	Region with the resource
10	Herb Gatherer's Camp	Medicine Production	1	500	1	100	5	—	6	Region with the resource
11	Obsidian Quarry	Obsidian Quarry	1	500	1	100	5	—	6	Region with the resource
12	Spice Market	Spice Trading	1	500	1	100	5	—	6	Region with the resource
13	Animal Store	Tusks	1	500	1	100	5	—	6	Region with the resource
14	Tailors' Guild	Industry	3	2,500	3	500	5	20	8	Any settlement
15	Cinnabar Mining Pit	Dye Production	1	500	1	100	5	—	6	Region with the resource
16	Iron Mining Pit	Iron Mining	1	500	2	100	5	—	7	Region with the resource
17	Stone Cutter	Marble Quarry	1	500	1	100	5	—	6	Region with the resource
18	Grazing Pastures	Pastures	1	500	1	100	5	—	6	Region with the resource
19	Clay Pit	Pottery Production	1	500	1	100	5	—	6	Region with the resource
20	Brine Mining Pit	Saltmaking	1	500	1	100	5	—	6	Region with the resource
21	Woodman's Hut	Woodlands	1	500	1	100	5	—	6	Region with the resource
22	Orchards	Orchards	1	500	1	100	5	—	6	Region with the resource
23	Exotic Animal Pen	Exotic Animals	2	1,000	2	150	6.70	20	8.70	Region with the resource
24	Exotic Hothouse	Medicine Production	2	1,000	2	150	6.70	20	8.70	Region with the resource
25	Obsidian Trinket Maker	Obsidian Quarry	2	1,000	2	150	6.70	20	8.70	Region with the resource
26	Spice Trading Post	Spice Trading	2	1,000	2	150	6.70	20	8.70	Region with the resource
27	Tusk Market	Tusks	2	1,000	2	150	6.70	20	8.70	Region with the resource
28	Cinnabar Mine	Dye Production	2	1,000	2	150	6.70	20	8.70	Region with the resource
29	Iron Mine	Iron Mining	2	1,000	3	150	6.70	20	9.70	Region with the resource
30	Marble Quarry	Marble Quarry	2	1,000	2	150	6.70	20	8.70	Region with the resource
31	Livestock Pens	Pastures	2	1,000	2	150	6.70	20	8.70	Region with the resource
32	Pottery Maker	Pottery Production	2	1,000	2	150	6.70	20	8.70	Region with the resource
33	Brine Mine	Saltmaking	2	1,000	2	150	6.70	20	8.70	Region with the resource
34	Timber Mill	Woodlands	2	1,000	2	150	6.70	20	8.70	Region with the resource
35	Vineyard	Orchards	2	1,000	2	150	6.70	20	8.70	Region with the resource
36	Estalian Harbour	Port	2	2,000	2	300	6.70	10	8.70	Port settlement
37	Estalian Trading Port	Port	3	4,000	3	500	8	20	11	Port settlement
38	Exotic Animal Market	Exotic Animals	3	2,000	3	200	10	40	13	Region with the resource
39	Alchemy Workshop	Medicine Production	3	2,000	3	200	10	40	13	Region with the resource
40	Obsidian Amulet Carver	Obsidian Quarry	3	2,000	3	200	10	40	13	Region with the resource
41	Eastern Bazaar	Spice Trading	3	2,000	3	200	10	40	13	Region with the resource
42	Tusk Compound	Tusks	3	2,000	3	200	10	40	13	Region with the resource
43	Imperial Harbour	Port	2	3,000	4	300	10	15	14	Port settlement
44	Dyemaker	Dye Production	3	2,000	3	200	10	40	13	Region with the resource
45	Iron Smelter	Iron Mining	3	2,000	4	200	10	40	14	Region with the resource
46	Mason	Marble Quarry	3	2,000	3	200	10	40	13	Region with the resource
47	Cattle Ranch	Pastures	3	2,000	3	200	10	40	13	Region with the resource
48	Kilns	Pottery Production	3	2,000	3	200	10	40	13	Region with the resource
49	Saltworks	Saltmaking	3	2,000	3	200	10	40	13	Region with the resource
50	Lumberyard	Woodlands	3	2,000	3	200	10	40	13	Region with the resource
51	Vintner	Orchards	3	2,000	3	200	10	40	13	Region with the resource
52	Estalian Docks	Port	1	1,000	1	100	10	—	11	Port settlement
53	Imperial Port	Port	3	6,000	6	500	12	30	18	Port settlement
54	Imperial Wharf	Port	1	1,500	2	100	15	—	17	Port settlement

Main building levels

Settlement upgrades make gold too, but they also cost growth (population surplus) and open building slots, so payback alone undersells them. Province capitals and minor settlements are separate chains.

#
1	Hamlet	Provincial Capital	1	1,000	—	40	—
2	Hamlet	Minor Settlement	1	1,000	—	40	—
3	Village	Provincial Capital	2	2,000	1	60	100
4	Village	Minor Settlement	2	2,000	1	60	100
5	Town	Provincial Capital	3	4,000	2	80	200
6	Town	Minor Settlement	3	4,000	2	80	200
7	City	Provincial Capital	4	8,000	4	100	400
8	City-State	Provincial Capital	5	16,000	5	120	800

Percentage income boosts

These add a share to other buildings' income: the province's, every region's you own, or the local region's (the region the building stands in). One pays back in 10 turns when the buildings it boosts make cost ÷ (10 × share) gold a turn — the last column.

#
1	Toll Gates	Transportation	4,500	8%	—	—	5,625
2	Paved Roads	Transportation	3,000	4%	—	—	7,500

Every level's full effects: The Empire buildings.