diff --git a/app/game-api/src/turns/commandInput.ts b/app/game-api/src/turns/commandInput.ts
index e0bffabe..69d3491a 100644
--- a/app/game-api/src/turns/commandInput.ts
+++ b/app/game-api/src/turns/commandInput.ts
@@ -80,6 +80,7 @@ export interface TurnCommandInputField {
     min?: number;
     max?: number;
     step?: number;
+    defaultValue?: TurnCommandOptionValue | boolean;
     constValue?: TurnCommandOptionValue;
     options?: TurnCommandOption[];
     optionSource?: TurnCommandOptionSource;
diff --git a/app/game-api/src/turns/commandTable.ts b/app/game-api/src/turns/commandTable.ts
index 4c27abb6..fc419b21 100644
--- a/app/game-api/src/turns/commandTable.ts
+++ b/app/game-api/src/turns/commandTable.ts
@@ -18,7 +18,7 @@ import type {
     TriggerValue,
     UnitSetDefinition,
 } from '@sammo-ts/logic';
-import { evaluateConstraints, LEGACY_DEFAULT_MAX_LEVEL } from '@sammo-ts/logic';
+import { evaluateConstraints, LEGACY_DEFAULT_MAX_LEVEL, resolveNonAggressionMaxEndYear } from '@sammo-ts/logic';
 import type { GeneralActionModule } from '@sammo-ts/logic/actionModules/general.js';
 import { CommandResolver as RecruitmentCommandResolver } from '@sammo-ts/logic/actions/turn/general/che_징병.js';
 import { projectItemSlots, readItemInventoryFromMeta } from '@sammo-ts/logic/items/index.js';
@@ -656,18 +656,33 @@ const FOUNDING_COMMAND_KEYS = new Set(['che_건국', 'cr_건국', 'che_무작위
 const buildEntries = (
     env: CommandEnv,
     specs: TurnCommandSpec[],
-    options: { foundingAvailable?: boolean } = {}
+    options: { foundingAvailable?: boolean; currentYear?: number; currentMonth?: number } = {}
 ): CommandEntry[] => {
     const entries: CommandEntry[] = [];
 
     for (const spec of specs) {
         const definition = spec.createDefinition(env);
+        const inputFields = buildTurnCommandInputFields(spec).map((field) => {
+            if (spec.key !== 'che_불가침제의') return field;
+            if (field.key === 'year' && options.currentYear !== undefined) {
+                return {
+                    ...field,
+                    min: options.currentYear + 1,
+                    max: resolveNonAggressionMaxEndYear(options.currentYear),
+                    defaultValue: options.currentYear + 1,
+                };
+            }
+            if (field.key === 'month' && options.currentMonth !== undefined) {
+                return { ...field, defaultValue: options.currentMonth };
+            }
+            return field;
+        });
         const entry: CommandEntry = {
             category: spec.category,
             definition,
             reqArg: spec.reqArg,
             availabilityArgs: spec.reqArg ? spec.availabilityArgs : {},
-            inputFields: buildTurnCommandInputFields(spec),
+            inputFields,
         };
 
         if (spec.key === 'che_포상') {
@@ -817,7 +832,10 @@ export const buildTurnCommandTable = async (options: {
                 ? undefined
                 : options.realNationCount < resolveMaxNation(options.worldState),
     });
-    const nationEntries = buildEntries(env, nationSpecs);
+    const nationEntries = buildEntries(env, nationSpecs, {
+        currentYear: options.worldState.currentYear,
+        currentMonth: options.worldState.currentMonth,
+    });
 
     return {
         general: buildGroups(
diff --git a/app/game-api/test/commandTable.test.ts b/app/game-api/test/commandTable.test.ts
index c26aa5d9..0236c799 100644
--- a/app/game-api/test/commandTable.test.ts
+++ b/app/game-api/test/commandTable.test.ts
@@ -337,6 +337,27 @@ describe('buildTurnCommandTable', () => {
         }
     });
 
+    it('projects the Ref twenty-year non-aggression end-year window', async () => {
+        const table = await buildTurnCommandTable({
+            worldState: buildWorldState(),
+            general: buildGeneral(),
+            city: buildCity(),
+            nation: buildNation(),
+            nationGenerals: null,
+        });
+        const proposal = table.nation
+            .flatMap((group) => group.values)
+            .find((command) => command.key === 'che_불가침제의');
+
+        expect(proposal?.inputFields.find((field) => field.key === 'year')).toMatchObject({
+            kind: 'number',
+            min: 4,
+            max: 23,
+            defaultValue: 4,
+        });
+        expect(proposal?.inputFields.find((field) => field.key === 'month')).toMatchObject({ defaultValue: 1 });
+    });
+
     it('projects the Ref availability boundaries for force move, retirement, and resignation', async () => {
         const buildTable = (general: GeneralRow, nation: NationRow | null = buildNation()) =>
             buildTurnCommandTable({
diff --git a/app/game-api/test/router.test.ts b/app/game-api/test/router.test.ts
index 02d5df3d..93f9761d 100644
--- a/app/game-api/test/router.test.ts
+++ b/app/game-api/test/router.test.ts
@@ -1462,6 +1462,28 @@ describe('appRouter', () => {
             })
         ).resolves.toMatchObject({ ok: true });
         expect(validTermWrites).toHaveLength(1);
+
+        const excessiveTermWrites: unknown[] = [];
+        const excessiveTermCaller = appRouter.createCaller(
+            buildContext({
+                state: buildWorldState(),
+                general,
+                nationTurnWrites: excessiveTermWrites,
+            })
+        );
+        await expect(
+            excessiveTermCaller.turns.reserved.setNation({
+                generalId: general.id,
+                turnIndex: 0,
+                action: 'che_불가침제의',
+                args: { destNationId: 2, year: 211, month: 1 },
+                expectedRevision: 0,
+            })
+        ).rejects.toMatchObject({
+            code: 'PRECONDITION_FAILED',
+            message: expect.stringContaining('기한은 210년 이하'),
+        });
+        expect(excessiveTermWrites).toHaveLength(0);
     });
 
     it('validates every bulk reservation permission before writing any turn', async () => {
diff --git a/app/game-engine/src/turn/ai/generalAi/nation/diplomacy.ts b/app/game-engine/src/turn/ai/generalAi/nation/diplomacy.ts
index 4de18ed5..bb430298 100644
--- a/app/game-engine/src/turn/ai/generalAi/nation/diplomacy.ts
+++ b/app/game-engine/src/turn/ai/generalAi/nation/diplomacy.ts
@@ -1,6 +1,6 @@
 import type { GeneralAI } from '../core.js';
 import { asRecord, joinYearMonth, parseYearMonth, readMetaNumber } from '../../aiUtils.js';
-import { resolveDiplomacyMessageValidUntilTick } from '@sammo-ts/logic';
+import { resolveDiplomacyMessageValidUntilTick, resolveNonAggressionMaxEndYear } from '@sammo-ts/logic';
 import { isNeighbor } from '@sammo-ts/logic/world/distance.js';
 import { resolveNationIncome } from './helpers.js';
 
@@ -99,7 +99,8 @@ export const do불가침제의 = (ai: GeneralAI) => {
         return null;
     }
 
-    const [targetYear, targetMonth] = parseYearMonth(Math.floor(yearMonth + diplomatMonth));
+    const maxEndMonth = joinYearMonth(resolveNonAggressionMaxEndYear(ai.world.currentYear), 12);
+    const [targetYear, targetMonth] = parseYearMonth(Math.min(Math.floor(yearMonth + diplomatMonth), maxEndMonth));
     const result = ai.buildNationCandidate(
         'che_불가침제의',
         { destNationId, year: targetYear, month: targetMonth },
diff --git a/app/game-engine/test/npcAidNonAggressionLifecycle.test.ts b/app/game-engine/test/npcAidNonAggressionLifecycle.test.ts
index 232f269a..6417dc2e 100644
--- a/app/game-engine/test/npcAidNonAggressionLifecycle.test.ts
+++ b/app/game-engine/test/npcAidNonAggressionLifecycle.test.ts
@@ -144,6 +144,7 @@ describe('NPC 원조 기반 불가침 제의 lifecycle', () => {
             .peekDirtyState()
             .messages.filter((message) => message.msgType === 'diplomacy' && message.option?.action === 'noAggression');
         expect(firstMessages).toHaveLength(1);
+        expect(firstMessages[0]?.option).toMatchObject({ year: 210, month: 12 });
         const tryEntry = (world.getNationById(1)!.meta.resp_assist_try as Record<string, number[]>).n2!;
         expect(tryEntry).toHaveLength(3);
         const validUntilTick = tryEntry[2]!;
diff --git a/app/game-frontend/e2e/commandArguments.spec.ts b/app/game-frontend/e2e/commandArguments.spec.ts
index 5746fcd1..2b50b2d5 100644
--- a/app/game-frontend/e2e/commandArguments.spec.ts
+++ b/app/game-frontend/e2e/commandArguments.spec.ts
@@ -504,7 +504,32 @@ const commandTable = {
                         },
                     ],
                 },
-                buildNationCommand('che_불가침제의', '불가침 제의'),
+                {
+                    ...buildNationCommand('che_불가침제의', '불가침 제의'),
+                    inputFields: [
+                        ...buildNationCommand('che_불가침제의', '불가침 제의').inputFields,
+                        {
+                            key: 'year',
+                            label: '기간(년)',
+                            kind: 'number',
+                            required: true,
+                            min: 191,
+                            max: 210,
+                            step: 1,
+                            defaultValue: 191,
+                        },
+                        {
+                            key: 'month',
+                            label: '기간(월)',
+                            kind: 'number',
+                            required: true,
+                            min: 1,
+                            max: 12,
+                            step: 1,
+                            defaultValue: 1,
+                        },
+                    ],
+                },
                 buildNationCommand('che_선전포고', '선전포고'),
                 buildNationCommand('che_종전제의', '종전 제의'),
                 buildNationCommand('che_불가침파기제의', '불가침 파기 제의'),
@@ -2158,6 +2183,42 @@ test('touch command maps select city and nation on the first tap without changin
     }
 });
 
+test('limits non-aggression end years to the Ref twenty-year window on desktop and mobile', async ({
+    browser,
+}, testInfo) => {
+    for (const viewport of [
+        { name: 'desktop', width: 1200, height: 900 },
+        { name: 'mobile', width: 500, height: 900 },
+    ]) {
+        const context = await browser.newContext({ viewport });
+        const page = await context.newPage();
+        try {
+            await install(page);
+            await page.goto('/che/chief-center');
+            await page.getByRole('button', { name: '1턴 명령 입력', exact: true }).click();
+            const picker = page.getByTestId('command-picker');
+            await picker.getByRole('button', { name: /^(?:국가:)?외교$/, exact: true }).click();
+            await picker.getByRole('button', { name: /불가침 제의/ }).click();
+
+            const form = picker.getByTestId('command-argument-form');
+            const yearInput = form.locator('#command-arg-year');
+            await expect(yearInput).toHaveAttribute('min', '191');
+            await expect(yearInput).toHaveAttribute('max', '210');
+            await expect(yearInput).toHaveValue('191');
+
+            const submit = picker.getByRole('button', { name: '입력', exact: true });
+            await yearInput.fill('211');
+            await expect(submit).toBeDisabled();
+            await yearInput.fill('210');
+            await expect(submit).toBeEnabled();
+
+            await picker.screenshot({ path: testInfo.outputPath(`non-aggression-year-limit-${viewport.name}.png`) });
+        } finally {
+            await context.close();
+        }
+    }
+});
+
 test('shows a map and target details for every city or nation argument chief command except assignment', async ({
     page,
 }) => {
@@ -2544,7 +2605,9 @@ test('keeps the entered command visible and reports a server validation error',
     await expect(page.getByRole('alert')).toContainText('대상 도시를 선택할 수 없습니다.');
     await expect(page.getByTestId('command-argument-form').locator('select')).toHaveValue('2');
     await expect(submit).toBeEnabled();
-    await expect(page.getByTestId('command-picker').getByRole('button', { name: '저장 중', exact: true })).toHaveCount(0);
+    await expect(page.getByTestId('command-picker').getByRole('button', { name: '저장 중', exact: true })).toHaveCount(
+        0
+    );
 });
 
 test('keeps Ref command briefs and autonomous-action state after a turn mutation', async ({ page, context }) => {
diff --git a/app/game-frontend/src/components/command/types.ts b/app/game-frontend/src/components/command/types.ts
index 2f6615f5..343a09fb 100644
--- a/app/game-frontend/src/components/command/types.ts
+++ b/app/game-frontend/src/components/command/types.ts
@@ -54,6 +54,7 @@ export type CommandInputField = {
     min?: number;
     max?: number;
     step?: number;
+    defaultValue?: string | number | boolean;
     constValue?: string | number;
     options?: CommandOption[];
     optionSource?: 'cities' | 'nations' | 'generals' | 'crewTypes' | 'armTypes' | 'nationTypes' | 'colors' | 'items';
diff --git a/app/game-frontend/src/components/main/CommandArgumentForm.vue b/app/game-frontend/src/components/main/CommandArgumentForm.vue
index b1a3e97b..8d041b5f 100644
--- a/app/game-frontend/src/components/main/CommandArgumentForm.vue
+++ b/app/game-frontend/src/components/main/CommandArgumentForm.vue
@@ -78,6 +78,7 @@ const optionsFor = (field: CommandInputField): CommandOption[] => {
 
 const defaultValue = (field: CommandInputField): unknown => {
     if (field.kind === 'hidden') return field.constValue;
+    if (field.defaultValue !== undefined) return field.defaultValue;
     if (field.kind === 'boolean') return true;
     if (field.kind === 'numberTuple') {
         const value = amountPreset.value?.defaultValue ?? field.min ?? 0;
diff --git a/packages/logic/src/actions/turn/nation/che_불가침제의.ts b/packages/logic/src/actions/turn/nation/che_불가침제의.ts
index 2edd4221..af25b50d 100644
--- a/packages/logic/src/actions/turn/nation/che_불가침제의.ts
+++ b/packages/logic/src/actions/turn/nation/che_불가침제의.ts
@@ -19,6 +19,7 @@ import type { NationTurnCommandSpec } from './index.js';
 import { z } from 'zod';
 import { parseArgsWithSchema } from '../parseArgs.js';
 import { resolveDiplomacyMessageValidMinutes } from '../../../diplomacy/messageValidity.js';
+import { NON_AGGRESSION_MIN_TERM_MONTHS, resolveNonAggressionMaxEndYear } from '../../../diplomacy/treatyTerm.js';
 import { resolveMessageTargetIcon } from '@sammo-ts/logic/messages/message.js';
 
 const ARGS_SCHEMA = z.object({
@@ -38,12 +39,11 @@ interface NonAggressionProposalContext<
 }
 
 const ACTION_NAME = '불가침 제의';
-const MIN_TERM_MONTHS = 6;
 
 const resolveMonthIndex = (year: number, month: number): number => year * 12 + month - 1;
 
-const reqMinimumTreatyTerm = (minMonths: number): Constraint => ({
-    name: 'reqMinimumTreatyTerm',
+const reqTreatyTermRange = (minMonths: number): Constraint => ({
+    name: 'reqTreatyTermRange',
     requires: () => [
         { kind: 'arg', key: 'year' },
         { kind: 'arg', key: 'month' },
@@ -100,6 +100,13 @@ const reqMinimumTreatyTerm = (minMonths: number): Constraint => ({
                 reason: `기한은 ${minMonths}개월 이상이어야 합니다.`,
             };
         }
+        const maxEndYear = resolveNonAggressionMaxEndYear(envYearValue);
+        if (yearValue > maxEndYear) {
+            return {
+                kind: 'deny',
+                reason: `기한은 ${maxEndYear}년 이하여야 합니다.`,
+            };
+        }
         return allow();
     },
 });
@@ -120,7 +127,7 @@ export class ActionDefinition<
     }
 
     buildPermissionConstraints(_ctx: ConstraintContext, _args: NonAggressionProposalArgs): Constraint[] {
-        return [reqMinimumTreatyTerm(MIN_TERM_MONTHS)];
+        return [reqTreatyTermRange(NON_AGGRESSION_MIN_TERM_MONTHS)];
     }
 
     buildMinConstraints(_ctx: ConstraintContext, _args: NonAggressionProposalArgs): Constraint[] {
@@ -133,7 +140,7 @@ export class ActionDefinition<
             notBeNeutral(),
             existsDestNation(),
             differentDestNation(),
-            reqMinimumTreatyTerm(MIN_TERM_MONTHS),
+            reqTreatyTermRange(NON_AGGRESSION_MIN_TERM_MONTHS),
             disallowDiplomacyBetweenStatus({
                 0: '아국과 이미 교전중입니다.',
                 1: '아국과 이미 선포중입니다.',
diff --git a/packages/logic/src/diplomacy/index.ts b/packages/logic/src/diplomacy/index.ts
index 668f91d6..ab928b2b 100644
--- a/packages/logic/src/diplomacy/index.ts
+++ b/packages/logic/src/diplomacy/index.ts
@@ -149,3 +149,4 @@ export const processDiplomacyMonth = (
 export * from './frontState.js';
 export * from './instantResponse.js';
 export * from './messageValidity.js';
+export * from './treatyTerm.js';
diff --git a/packages/logic/src/diplomacy/treatyTerm.ts b/packages/logic/src/diplomacy/treatyTerm.ts
new file mode 100644
index 00000000..d96ec85d
--- /dev/null
+++ b/packages/logic/src/diplomacy/treatyTerm.ts
@@ -0,0 +1,5 @@
+export const NON_AGGRESSION_MIN_TERM_MONTHS = 6;
+export const NON_AGGRESSION_MAX_END_YEAR_OFFSET = 20;
+
+export const resolveNonAggressionMaxEndYear = (currentYear: number): number =>
+    currentYear + NON_AGGRESSION_MAX_END_YEAR_OFFSET;
diff --git a/packages/logic/test/actions/turn/reservationPermission.test.ts b/packages/logic/test/actions/turn/reservationPermission.test.ts
index f23d2b04..b8b5dfb6 100644
--- a/packages/logic/test/actions/turn/reservationPermission.test.ts
+++ b/packages/logic/test/actions/turn/reservationPermission.test.ts
@@ -146,7 +146,7 @@ describe('legacy reservation permission constraints', () => {
         ).toEqual({ kind: 'allow' });
     });
 
-    it('checks only the six-month minimum when reserving a non-aggression proposal', () => {
+    it('keeps non-aggression proposals between the six-month minimum and Ref twenty-year limit', () => {
         const definition = new NonAggressionProposalAction();
         const shortArgs = { destNationId: 2, year: 190, month: 6 };
         expect(
@@ -162,5 +162,23 @@ describe('legacy reservation permission constraints', () => {
         ).toEqual({
             kind: 'allow',
         });
+
+        const maxTermArgs = { destNationId: 2, year: 210, month: 12 };
+        expect(
+            evaluatePermission(definition.buildPermissionConstraints(permissionContext, maxTermArgs), maxTermArgs)
+        ).toEqual({
+            kind: 'allow',
+        });
+
+        const excessiveTermArgs = { destNationId: 2, year: 211, month: 1 };
+        expect(
+            evaluatePermission(
+                definition.buildPermissionConstraints(permissionContext, excessiveTermArgs),
+                excessiveTermArgs
+            )
+        ).toMatchObject({
+            kind: 'deny',
+            reason: '기한은 210년 이하여야 합니다.',
+        });
     });
 });