diff --git a/core/src/Effect.cpp b/core/src/Effect.cpp
index 87beb2e..fea5573 100644
--- a/core/src/Effect.cpp
+++ b/core/src/Effect.cpp
@@ -181,3 +181,54 @@ EffectModifier effectModifiers(const EffectSet& set) {
     return modifier;
 }
 
+EffectSet::Pending tickEffects(EffectSet& set) {
+    EffectSet::Pending pending;
+    for (EffectInstance& effect : set.active) {
+        if (effect.durationTicks <= 0) continue;
+        switch (effect.kind) {
+            case EffectKind::InstantHealth:
+                pending.instantHeal +=
+                    static_cast<float>(4 << std::min(effect.amplifier, 8)) * effect.potency;
+                break;
+            case EffectKind::InstantDamage:
+                pending.instantDamage +=
+                    static_cast<float>(6 << std::min(effect.amplifier, 8)) * effect.potency;
+                break;
+            default: break;
+        }
+        int interval = periodicIntervalTicks(effect.kind, effect.amplifier);
+        if (interval > 0 && effect.durationTicks % interval == 0) {
+            switch (effect.kind) {
+                case EffectKind::Regeneration: pending.regenerationHeal += 1.0f; break;
+                case EffectKind::Poison:       pending.poisonDamage += 1.0f; break;
+                case EffectKind::Wither:       pending.witherDamage += 1.0f; break;
+                case EffectKind::Saturation:
+                    pending.saturationGain += static_cast<float>(effect.level());
+                    break;
+                default: break;
+            }
+        }
+        --effect.durationTicks;
+    }
+    std::size_t before = set.active.size();
+    set.active.erase(std::remove_if(set.active.begin(), set.active.end(),
+                                    [](const EffectInstance& e) { return e.durationTicks <= 0; }),
+                     set.active.end());
+    pending.expiredCount = static_cast<int>(before - set.active.size());
+    return pending;
+}
+
+float applyEffectTick(const EffectSet::Pending& pending, float& health, float maxHealth) {
+    float before = health;
+    float heal = pending.regenerationHeal + pending.instantHeal;
+    if (heal > 0.0f) health = std::min(maxHealth, health + heal);
+    if (pending.poisonDamage > 0.0f) {
+        float survivable = clampZero(health - 1.0f);
+        health -= std::min(pending.poisonDamage, survivable);
+    }
+    float lethal = pending.witherDamage + pending.instantDamage;
+    if (lethal > 0.0f) health = clampZero(health - lethal);
+    return health - before;
+}
+
+} // namespace vf