Key takeaways
- Expected damage per second is damage × attacks per second × (1 + crit chance × (crit multiplier − 1)).
- Damage and attack speed multiply, so splitting upgrades between them beats stacking one: +20% of each gives 1.44×, while +40% of one gives 1.4×.
- Critical damage upgrades are weak while crit chance is low; raise the chance first, then the multiplier.
- Range adds shots: on a path straight through a tower's circle, 20% more range means about 20% more time in range.
- Read the fight first: the right upgrade is the one that fixes what actually broke, as Hero TD's listing advises.
Idle tower defense games hand you a steady stream of upgrades and a simple question: what next? Damage, attack speed, critical hits, range, the castle or the hero? This guide answers it with arithmetic rather than rules of thumb, using a simple model of a tower. The numbers are illustrative, not taken from any particular game; check how your own game's upgrades stack before applying them.
Start by reading the fight
Before any formula, look at what went wrong. Hero TD Idle Tower Defense's Google Play listing puts it well: "look at how your towers perform", decide which upgrades matter next, and choose them "with a purpose rather than spending without a strategy." As general reasoning, different symptoms point to different fixes:
| What you see | Likely fix |
|---|---|
| Enemies die just short of the castle | A little more damage per second |
| Enemies pass towers before many shots land | Range |
| A few enemies reach the castle every wave | Castle defense, as insurance |
| One big wave breaks through at once | The hero's spells or ultimate |
The formula behind damage
For a tower that attacks repeatedly, expected damage per second (DPS) is:
DPS = damage × attacks per second × (1 + crit chance × (crit multiplier − 1))
The last bracket is the average boost from critical hits. Wikipedia notes that critical hits are meant to simulate an occasional "lucky hit" and are almost always random; the 1986 game Dragon Quest brought them into video games at a fixed rate of 1/64, about 1.56%. Wikipedia adds that many other games using critical hits may have ways of increasing how likely they are.
A worked tower. Damage 100, one attack a second, 10% crit chance, 2× crit multiplier:
DPS = 100 × 1 × (1 + 0.10 × 1) = 110.
Damage or attack speed?
Now compare four upgrades that might cost about the same:
| Upgrade | New DPS | Gain |
|---|---|---|
| +20% damage (120) | 132 | +20% |
| +20% attack speed (1.2 a second) | 132 | +20% |
| Crit chance 10% → 20% | 120 | +9% |
| Crit multiplier 2× → 2.5× | 115 | +5% |
Damage and attack speed tie, because both multiply the same total. The difference shows when you buy several. Because they multiply, balanced upgrades win: two +20% upgrades split one each give 1.2 × 1.2 = 1.44×, while both on damage give 1.4× (assuming each upgrade adds 20% of the base value). The more upgrades you buy, the bigger that gap becomes, so keep the two roughly level unless a game prices one much more cheaply.
When critical hits pay off
Critical upgrades look weak in the table, but only because the crit chance is low. The two crit stats also multiply each other inside the bracket. Push the chance to 50% and the multiplier upgrade from 2× to 2.5× is worth much more: the bracket rises from 1.5 to 1.75, a gain of about 17%, against about 5% at a 10% chance. The order is clear: build crit chance first, then crit damage.
Range: more shots per enemy
Range works differently. It does not make a tower hit harder; it gives the tower more time to shoot. If an enemy walks straight through the middle of a tower's range circle, it stays in range for a distance of twice the radius. Time in range is that distance divided by the enemy's speed, so 20% more range means about 20% more shots at every passing enemy. Paths that clip the edge of the circle gain more or less, depending on the angle, and range is worth little if enemies already die on entry. For placement around paths, tower defense strategy basics covers the geometry, and tower types and what they counter the roles.
The castle: insurance, not a fix
Castle defense, and in Hero TD wall upgrades and emergency repairs, do not kill anything. They raise how many leaks you can survive. That makes them the right buy when a handful of enemies get through each wave and your damage is close to enough: the extra health buys time for the next damage upgrade. If whole waves break through, more wall only delays the loss.
Where the hero fits
In Hero TD, the hero is a mobile answer to the moments a wave gets through, with skills, spells such as fireballs and an ultimate ability; the store screenshots also show an armoury of weapons, armour, helmets, boots, rings and relics. As general reasoning, a unit that can move suits problems that towers in fixed positions handle badly, such as a sudden surge. The Hero TD guide explains the hero and modes.
A simple priority order
- Read the fight and name the problem.
- Keep damage and attack speed roughly balanced on the towers doing the most work.
- Add range where enemies pass before towers fire much.
- Raise crit chance before crit damage.
- Buy castle defense when small leaks are the only problem.
Hero TD Idle Tower Defense is one of our action and arcade games; its upgrades cover damage, attack speed, critical hits, range and castle defense. What idle games are explains how upgrade loops work across the wider genre.
Good to know
Frequently asked questions
Should I upgrade damage or attack speed first?
When are critical hit upgrades worth it?
Is range worth upgrading in tower defense?
When should I upgrade the castle?
Sources
- Critical hit (opens in a new tab)Wikipedia — accessed
- Tower defense (opens in a new tab)Wikipedia — accessed
- Hero TD Idle Tower Defense (opens in a new tab)Google Play — accessed
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