diff --git a/client/src/components/LogEntryEditor.tsx b/client/src/components/LogEntryEditor.tsx
index 591f435..f6fe772 100644
--- a/client/src/components/LogEntryEditor.tsx
+++ b/client/src/components/LogEntryEditor.tsx
@@ -43,7 +43,13 @@ import { computeTrackStats, formatTrackStats } from '../utils/trackStats.js'
 import { computeFuelPerMotorHour, formatFuelPerMotorHour } from '../utils/fuelStats.js'
 import { useRegisterUnsavedChanges } from '../context/UnsavedChangesContext.tsx'
 import TankLiterInput from './TankLiterInput.tsx'
-import { extractTankCapacitiesFromYacht, type VesselTankCapacities } from '../utils/tankCapacity.js'
+import {
+  computeEveningTankMaxLiters,
+  computeRefilledTankMaxLiters,
+  extractTankCapacitiesFromYacht,
+  formatTankLitersForInput,
+  type VesselTankCapacities
+} from '../utils/tankCapacity.js'
 
 function emptyTankLevels() {
   return { morning: 0, refilled: 0, evening: 0, consumption: 0 }
@@ -279,6 +285,36 @@ export default function LogEntryEditor({
 
   const tankCapacityTooltip = t('logs.tank_capacity_tooltip')
 
+  const fwRefilledMax = useMemo(
+    () => computeRefilledTankMaxLiters(fwMorning, tankCapacities.freshwaterCapacityL),
+    [fwMorning, tankCapacities.freshwaterCapacityL]
+  )
+
+  const fwEveningMax = useMemo(
+    () =>
+      computeEveningTankMaxLiters(
+        fwMorning,
+        fwRefilled,
+        tankCapacities.freshwaterCapacityL
+      ),
+    [fwMorning, fwRefilled, tankCapacities.freshwaterCapacityL]
+  )
+
+  const fuelRefilledMax = useMemo(
+    () => computeRefilledTankMaxLiters(fuelMorning, tankCapacities.fuelCapacityL),
+    [fuelMorning, tankCapacities.fuelCapacityL]
+  )
+
+  const fuelEveningMax = useMemo(
+    () =>
+      computeEveningTankMaxLiters(
+        fuelMorning,
+        fuelRefilled,
+        tankCapacities.fuelCapacityL
+      ),
+    [fuelMorning, fuelRefilled, tankCapacities.fuelCapacityL]
+  )
+
   const currentFingerprint = useMemo(() => {
     const payload = buildPayloadForSigning()
     return JSON.stringify({
@@ -538,6 +574,38 @@ export default function LogEntryEditor({
     setFuelConsumption(cons >= 0 ? String(cons) : '0')
   }, [fuelMorning, fuelRefilled, fuelEvening])
 
+  useEffect(() => {
+    if (fwRefilledMax == null) return
+    const refilled = parseFloat(fwRefilled) || 0
+    if (refilled > fwRefilledMax) {
+      setFwRefilled(formatTankLitersForInput(fwRefilledMax))
+    }
+  }, [fwRefilledMax, fwMorning])
+
+  useEffect(() => {
+    if (fwEveningMax == null) return
+    const evening = parseFloat(fwEvening) || 0
+    if (evening > fwEveningMax) {
+      setFwEvening(formatTankLitersForInput(fwEveningMax))
+    }
+  }, [fwEveningMax, fwMorning, fwRefilled])
+
+  useEffect(() => {
+    if (fuelRefilledMax == null) return
+    const refilled = parseFloat(fuelRefilled) || 0
+    if (refilled > fuelRefilledMax) {
+      setFuelRefilled(formatTankLitersForInput(fuelRefilledMax))
+    }
+  }, [fuelRefilledMax, fuelMorning])
+
+  useEffect(() => {
+    if (fuelEveningMax == null) return
+    const evening = parseFloat(fuelEvening) || 0
+    if (evening > fuelEveningMax) {
+      setFuelEvening(formatTankLitersForInput(fuelEveningMax))
+    }
+  }, [fuelEveningMax, fuelMorning, fuelRefilled])
+
   // Load yacht sails and tank capacities
   useEffect(() => {
     async function loadYachtMeta() {
@@ -1249,7 +1317,7 @@ export default function LogEntryEditor({
                 label={t('logs.refilled')}
                 value={fwRefilled}
                 onChange={setFwRefilled}
-                maxLiters={tankCapacities.freshwaterCapacityL}
+                maxLiters={fwRefilledMax ?? tankCapacities.freshwaterCapacityL}
                 disabled={saving || readOnly}
                 titleTooltip={tankCapacityTooltip}
               />
@@ -1258,7 +1326,7 @@ export default function LogEntryEditor({
                 label={t('logs.evening')}
                 value={fwEvening}
                 onChange={setFwEvening}
-                maxLiters={tankCapacities.freshwaterCapacityL}
+                maxLiters={fwEveningMax}
                 disabled={saving || readOnly}
                 titleTooltip={tankCapacityTooltip}
               />
@@ -1298,7 +1366,7 @@ export default function LogEntryEditor({
                 label={t('logs.refilled')}
                 value={fuelRefilled}
                 onChange={setFuelRefilled}
-                maxLiters={tankCapacities.fuelCapacityL}
+                maxLiters={fuelRefilledMax ?? tankCapacities.fuelCapacityL}
                 disabled={saving || readOnly}
                 titleTooltip={tankCapacityTooltip}
               />
@@ -1307,7 +1375,7 @@ export default function LogEntryEditor({
                 label={t('logs.evening')}
                 value={fuelEvening}
                 onChange={setFuelEvening}
-                maxLiters={tankCapacities.fuelCapacityL}
+                maxLiters={fuelEveningMax}
                 disabled={saving || readOnly}
                 titleTooltip={tankCapacityTooltip}
               />
diff --git a/client/src/utils/tankCapacity.test.ts b/client/src/utils/tankCapacity.test.ts
index c0705d9..a917360 100644
--- a/client/src/utils/tankCapacity.test.ts
+++ b/client/src/utils/tankCapacity.test.ts
@@ -1,6 +1,8 @@
 import { describe, expect, it } from 'vitest'
 import {
   clampTankLiters,
+  computeEveningTankMaxLiters,
+  computeRefilledTankMaxLiters,
   extractTankCapacitiesFromYacht,
   formatTankLitersForInput,
   parseOptionalTankLiters,
@@ -44,4 +46,17 @@ describe('tankCapacity', () => {
     expect(clampTankLiters(-5, 200)).toBe(0)
     expect(clampTankLiters(50)).toBe(50)
   })
+
+  it('computes refilled max as capacity minus morning', () => {
+    expect(computeRefilledTankMaxLiters('10', 60)).toBe(50)
+    expect(computeRefilledTankMaxLiters('60', 60)).toBeUndefined()
+    expect(computeRefilledTankMaxLiters('10', undefined)).toBeUndefined()
+  })
+
+  it('computes evening max as morning plus refilled capped by capacity', () => {
+    expect(computeEveningTankMaxLiters('10', '20', 60)).toBe(30)
+    expect(computeEveningTankMaxLiters('40', '40', 60)).toBe(60)
+    expect(computeEveningTankMaxLiters('10', '20')).toBe(30)
+    expect(computeEveningTankMaxLiters('0', '0', 60)).toBeUndefined()
+  })
 })
diff --git a/client/src/utils/tankCapacity.ts b/client/src/utils/tankCapacity.ts
index 81e0ee0..44a2833 100644
--- a/client/src/utils/tankCapacity.ts
+++ b/client/src/utils/tankCapacity.ts
@@ -50,6 +50,47 @@ export function extractTankCapacitiesFromYacht(decrypted: unknown): VesselTankCa
   return capacities
 }
 
+/** Parse a liter amount from form state (string). */
+export function parseTankLitersFromInput(input: string): number {
+  const trimmed = input.trim().replace(',', '.')
+  if (!trimmed) return 0
+  const parsed = Number(trimmed)
+  return Number.isFinite(parsed) && parsed >= 0 ? parsed : 0
+}
+
+/**
+ * Max for refilled amount: remaining capacity after morning level.
+ * Returns undefined when no positive max (no slider).
+ */
+export function computeRefilledTankMaxLiters(
+  morningInput: string,
+  tankCapacityL?: number
+): number | undefined {
+  if (tankCapacityL == null || tankCapacityL <= 0) return undefined
+  const remaining = tankCapacityL - parseTankLitersFromInput(morningInput)
+  if (remaining <= 0) return undefined
+  return remaining
+}
+
+/**
+ * Max for evening fill level: morning + refilled, capped by tank capacity when known.
+ * Returns undefined when no positive max (no slider).
+ */
+export function computeEveningTankMaxLiters(
+  morningInput: string,
+  refilledInput: string,
+  tankCapacityL?: number
+): number | undefined {
+  const sum = parseTankLitersFromInput(morningInput) + parseTankLitersFromInput(refilledInput)
+  if (sum <= 0) return undefined
+
+  if (tankCapacityL != null && tankCapacityL > 0) {
+    return Math.min(tankCapacityL, sum)
+  }
+
+  return sum
+}
+
 /** Clamp numeric liter value to [0, max] when max is known. */
 export function clampTankLiters(value: number, maxLiters?: number): number {
   const clamped = Math.max(0, value)