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Construction speed explained

How speed bonuses, Double Time and Zinman actually change an upgrade.

Updated 2026-10-14 · 3 min read

Construction speed is one of those numbers everyone pushes up without quite knowing what it does. "+100%" sounds like it should make an upgrade instant; in fact it halves it. And the buffs you switch on for a big upgrade don't all work the same way. Here's how they combine, with a real example: the Furnace's climb from FC8 to FC9, which takes 65 days with no bonuses at all.

Speed bonuses divide the time

Your construction speed (from research, gear, pets and so on) is added up into one percentage, and the base time is divided by one plus that number. So +50% turns 30 days into 20, +100% into 15 and +200% into 10. Each extra point of speed saves a little less time than the one before, which is why the first big chunk of construction speed matters most.

Temporary bonuses — the state's Mercantilism (+10%), the Vice President's buff (+10%) and pet skills such as the Hyena's Builder's Aide — are simply added to that percentage while they're active.

Double Time takes a slice off the end

Double Time works differently: it takes 20% off the time after all the speed bonuses are applied. That's why it's worth turning on for every long upgrade, even with high construction speed — it always saves a fifth.

Worked example: Furnace FC8 → FC9

Going from no bonuses to a typical mid-game setup cuts the climb from 65 days to under 24. The same rules apply to every building, so the building calculator lets you enter your own speed and switch Double Time on or off.

Zinman cuts resources, not crystals

Zinman's Resourceful skill reduces the Meat, Wood, Coal and Iron an upgrade costs by its percentage. It doesn't touch Fire Crystal or Refined Fire Crystal. Here's the same FC8 → FC9 climb at a few skill levels:

If the upgrade screen shows you less Meat than a calculator expects, this is usually why — at 12% the numbers drop by exactly that much.

Quick tips

• Start long upgrades when Double Time and any state buffs are active; the time is fixed when the upgrade begins.
• For SvS day 1, start the upgrade on the day — it doesn't have to finish. See the SvS prep plan.
• Speedups don't care about your speed bonus: an hour of speedup is always an hour off the timer, so a faster build needs fewer of them.

For the full cost of every Furnace level, see Furnace FC1 to FC10.

Try it with your numbers

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