diff --git a/client/scripts/size-baseline.json b/client/scripts/size-baseline.json
index b08cfde73..7489f9aba 100644
--- a/client/scripts/size-baseline.json
+++ b/client/scripts/size-baseline.json
@@ -3,7 +3,7 @@
   "src/api/client.ts": 1873,
   "src/components/Admin/AdminPluginsPanel.test.tsx": 2704,
   "src/components/Admin/AdminPluginsPanel.tsx": 1277,
-  "src/components/Budget/CostsPanel.test.tsx": 2736,
+  "src/components/Budget/CostsPanel.test.tsx": 2730,
   "src/components/Budget/CostsPanel.tsx": 1798,
   "src/components/Map/MapView.tsx": 1385,
   "src/components/Map/MapViewGL.test.tsx": 2919,
diff --git a/server/scripts/size-baseline.json b/server/scripts/size-baseline.json
index 631863b02..77a57d404 100644
--- a/server/scripts/size-baseline.json
+++ b/server/scripts/size-baseline.json
@@ -7,7 +7,7 @@
   "src/db/repositories/Users.repository.ts": 1445,
   "src/nest/atlas/atlas.service.ts": 1177,
   "src/nest/auth/auth.service.ts": 1143,
-  "src/nest/budget/budget.service.ts": 1617,
+  "src/nest/budget/budget.service.ts": 1613,
   "src/nest/collections/collections.service.ts": 1426,
   "src/nest/doc-sync/doc-sync.service.ts": 1060,
   "src/nest/doc-sync/providers/synology-drive.client.ts": 1160,
diff --git a/server/src/nest/budget/budget-money.helpers.ts b/server/src/nest/budget/budget-money.helpers.ts
index 1d18c76bf..9f1ecc19a 100644
--- a/server/src/nest/budget/budget-money.helpers.ts
+++ b/server/src/nest/budget/budget-money.helpers.ts
@@ -1,4 +1,4 @@
-import { splitEqualShares, sumMinor, toMinor } from '@trek/shared';
+import { currencyDecimals, splitEqualShares, sumMinor, toMinor } from '@trek/shared';
 
 /**
  * Re-denominate whole trip-currency cents into whole display-currency cents
@@ -164,3 +164,77 @@ export function quoteRatio(rates: Record<string, number> | null, to: string, fro
   const rFrom = rates?.[from];
   return rTo && rTo > 0 && rFrom && rFrom > 0 ? rTo / rFrom : null;
 }
+
+/**
+ * How a settlement reads its currencies: the display currency it answers in, the factor
+ * from trip cents into it, and the converters for expenses and recorded transfers.
+ * `calculateSettlement` nets with these; they are pure, so they live here.
+ */
+export function settlementFx(opts: {
+  base?: string;
+  rates?: Record<string, number> | null;
+  tripCurrency?: string;
+  baseRate?: number;
+}) {
+  const requested = (opts.base || opts.tripCurrency || 'EUR').toUpperCase();
+  const tripCurrency = (opts.tripCurrency || requested).toUpperCase();
+  const rates = opts.rates ?? null;
+  // Net the whole settlement in the trip's canonical currency and convert the final
+  // totals to the display currency once, instead of netting in the (moving) display
+  // currency. Otherwise per-expense rounding shifts as live FX drifts and the greedy
+  // debt-simplifier reshuffles it into phantom third-party micro-flows (#1382). When
+  // the display currency IS the trip currency (the common case) every conversion below
+  // is the identity, so behaviour is unchanged.
+  // rates[X] = units of X per 1 base; the frozen exchange_rate is units of item-currency
+  // per 1 trip-currency. Pre-rework rows store currency = NULL = "the trip's own currency".
+  // Prefer the FX rate frozen at entry time (#1335): a settled expense keeps the rate
+  // it was booked at, so a later live-rate drift doesn't re-open it with a residual.
+  // Legacy rows without a frozen rate convert via base with live rates.
+  const converterFor = (itemCurrency: string | null | undefined, itemRate?: number | null) =>
+    tripConverter(itemCurrency, itemRate, tripCurrency, rates);
+  // trip-currency → display currency, applied once to the final netted totals.
+  // Held as a plain factor so it is exactly linear: the balances are converted as
+  // one set (allocateDisplayCents) rather than one at a time, which is what keeps
+  // them adding up to zero in whatever currency the viewer picked (#1382).
+  //
+  // `rates` may be quoted against any base; the ratio of the two quotes is the
+  // factor either way. Callers pass the trip currency's own quote (see settlement()),
+  // the one freezeForeignRate froze every entry rate from, so a bill entered today in
+  // the display currency converts back to exactly what was typed (#2525). Taken the
+  // other way round, from the display currency's quote, the two quotes are not exact
+  // inverses and 12,345.67 USD came back as 12,346.06.
+  //
+  // Without a quote, the caller's own figure for the pair (`baseRate`) stands in for
+  // the missing display quote, and for nothing else: a row with a currency of its own
+  // is never converted with it. Like a live quote, it also reads a legacy transfer
+  // without a currency, which is taken to be in the display currency. With neither,
+  // the answer stays in the trip currency and says so, rather than printing trip cents
+  // as the display currency.
+  const baseRate = opts.baseRate != null && Number.isFinite(opts.baseRate) && opts.baseRate > 0 ? opts.baseRate : null;
+  const quoted = requested === tripCurrency ? 1 : (quoteRatio(rates, requested, tripCurrency) ?? baseRate);
+  const currency = quoted === null ? tripCurrency : requested;
+  const displayFactor = quoted ?? 1;
+  // Every figure goes out in whole steps of that currency: whole won or yen (#2604).
+  const displayUnit = 10 ** Math.max(0, 2 - currencyDecimals(currency));
+  const toDisplay = (cents: number[], total?: number) => allocateDisplayCents(cents, displayFactor, total, displayUnit);
+  // An expense entered in the display currency itself is owed in that currency
+  // (#2965). Booked through the trip currency at its frozen rate and back at
+  // today's, 1,081.09 EUR on a yen trip came back a day later as 1,078.86 EUR,
+  // and a repayment of exactly what was typed left 2.23 EUR owed. Such rows are
+  // netted apart, in whole display cents as entered; every other row still nets
+  // in trip cents and converts once, so Σ balances stays 0 in both halves.
+  const direct = currency !== tripCurrency ? currency : null;
+  const isDirect = (rowCurrency: string | null | undefined) =>
+    direct !== null && (rowCurrency || tripCurrency).toUpperCase() === direct;
+  // A recorded settle-up amount is entered in whatever display currency the payer
+  // was viewing. New rows capture that currency and the rate frozen at settle time
+  // (#1445), so a settled position stays balanced when live rates drift — mirroring
+  // the expenses; a frozen currency without a usable rate falls back to live rates,
+  // and without those the transfer is left out like an expense. Legacy rows
+  // (currency = NULL) have no frozen rate, so fall back to the old behaviour: assume
+  // they were entered in the current display base and convert with live rates, by the
+  // inverse of the display factor, so such a transfer reads back as entered.
+  const settleConverterFor = (sCurrency?: string | null, sRate?: number | null) =>
+    sCurrency ? tripConverter(sCurrency, sRate, tripCurrency, rates) : (amount: number) => amount / displayFactor;
+  return { currency, displayFactor, toDisplay, converterFor, settleConverterFor, isDirect };
+}
diff --git a/server/src/nest/budget/budget.service.ts b/server/src/nest/budget/budget.service.ts
index 130429986..3f7f1310e 100644
--- a/server/src/nest/budget/budget.service.ts
+++ b/server/src/nest/budget/budget.service.ts
@@ -1,7 +1,7 @@
 import { Injectable } from '@nestjs/common';
 import { InjectRepository } from '@mikro-orm/nestjs';
 import type { BudgetFallbackFx, BudgetParticipantFinal, BudgetUnconverted, TrekWsPayload, TrekWsTripEventName } from '@trek/shared';
-import { currencyDecimals, splitEqualShares, sumMinor, toMinor } from '@trek/shared';
+import { splitEqualShares, sumMinor, toMinor } from '@trek/shared';
 import { RealtimeService } from '../realtime/realtime.service';
 import { PermissionsService } from '../permissions/permissions.service';
 import { avatarUrl } from '../common/avatarUrl';
@@ -31,7 +31,7 @@ import { BUDGET_ITEM_TICKET, RESERVATION_METADATA } from '../../db/json-columns'
 import { decodeJson, decodeJsonResult, encodeJson } from '../../utils/json-column';
 import { DomainError } from '../common/domain-error';
 import { GUEST_HAS_PAYMENTS, shareAfterLeaving } from './budget-departure.helpers';
-import { allocateDisplayCents, customSplitCents, isFrozenRate, NOT_FROZEN_RATE, quoteRatio, summaryShareCents, sumMoney, tripConverter } from './budget-money.helpers';
+import { customSplitCents, isFrozenRate, NOT_FROZEN_RATE, settlementFx, summaryShareCents, sumMoney, tripConverter } from './budget-money.helpers';
 
 type Trip = TripAccess;
 
@@ -1083,68 +1083,7 @@ export class BudgetService {
     tripId: string | number,
     opts: { base?: string; rates?: Record<string, number> | null; tripCurrency?: string; baseRate?: number } = {},
   ) {
-    const requested = (opts.base || opts.tripCurrency || 'EUR').toUpperCase();
-    const tripCurrency = (opts.tripCurrency || requested).toUpperCase();
-    const rates = opts.rates ?? null;
-    // Net the whole settlement in the trip's canonical currency and convert the final
-    // totals to the display currency once, instead of netting in the (moving) display
-    // currency. Otherwise per-expense rounding shifts as live FX drifts and the greedy
-    // debt-simplifier reshuffles it into phantom third-party micro-flows (#1382). When
-    // the display currency IS the trip currency (the common case) every conversion below
-    // is the identity, so behaviour is unchanged.
-    // rates[X] = units of X per 1 base; the frozen exchange_rate is units of item-currency
-    // per 1 trip-currency. Pre-rework rows store currency = NULL = "the trip's own currency".
-    // Prefer the FX rate frozen at entry time (#1335): a settled expense keeps the rate
-    // it was booked at, so a later live-rate drift doesn't re-open it with a residual.
-    // Legacy rows without a frozen rate convert via base with live rates.
-    const converterFor = (itemCurrency: string | null | undefined, itemRate?: number | null) =>
-      tripConverter(itemCurrency, itemRate, tripCurrency, rates);
-    // trip-currency → display currency, applied once to the final netted totals.
-    // Held as a plain factor so it is exactly linear: the balances are converted as
-    // one set (allocateDisplayCents) rather than one at a time, which is what keeps
-    // them adding up to zero in whatever currency the viewer picked (#1382).
-    //
-    // `rates` may be quoted against any base; the ratio of the two quotes is the
-    // factor either way. Callers pass the trip currency's own quote (see settlement()),
-    // the one freezeForeignRate froze every entry rate from, so a bill entered today in
-    // the display currency converts back to exactly what was typed (#2525). Taken the
-    // other way round, from the display currency's quote, the two quotes are not exact
-    // inverses and 12,345.67 USD came back as 12,346.06.
-    //
-    // Without a quote, the caller's own figure for the pair (`baseRate`) stands in for
-    // the missing display quote, and for nothing else: a row with a currency of its own
-    // is never converted with it. Like a live quote, it also reads a legacy transfer
-    // without a currency, which is taken to be in the display currency. With neither,
-    // the answer stays in the trip currency and says so, rather than printing trip cents
-    // as the display currency.
-    const baseRate = opts.baseRate != null && Number.isFinite(opts.baseRate) && opts.baseRate > 0 ? opts.baseRate : null;
-    const quoted = requested === tripCurrency ? 1 : (quoteRatio(rates, requested, tripCurrency) ?? baseRate);
-    const currency = quoted === null ? tripCurrency : requested;
-    const displayFactor = quoted ?? 1;
-    // Every figure goes out in whole steps of that currency: whole won or yen (#2604).
-    const displayUnit = 10 ** Math.max(0, 2 - currencyDecimals(currency));
-    const toDisplay = (cents: number[], total?: number) => allocateDisplayCents(cents, displayFactor, total, displayUnit);
-    // An expense entered in the display currency itself is owed in that currency
-    // (#2965). Booked through the trip currency at its frozen rate and back at
-    // today's, 1,081.09 EUR on a yen trip came back a day later as 1,078.86 EUR,
-    // and a repayment of exactly what was typed left 2.23 EUR owed. Such rows are
-    // netted apart, in whole display cents as entered; every other row still nets
-    // in trip cents and converts once, so Σ balances stays 0 in both halves.
-    const direct = currency !== tripCurrency ? currency : null;
-    const isDirect = (rowCurrency: string | null | undefined) =>
-      direct !== null && (rowCurrency || tripCurrency).toUpperCase() === direct;
-    // A recorded settle-up amount is entered in whatever display currency the payer
-    // was viewing. New rows capture that currency and the rate frozen at settle time
-    // (#1445), so a settled position stays balanced when live rates drift — mirroring
-    // the expenses; a frozen currency without a usable rate falls back to live rates,
-    // and without those the transfer is left out like an expense. Legacy rows
-    // (currency = NULL) have no frozen rate, so fall back to the old behaviour: assume
-    // they were entered in the current display base and convert with live rates.
-    const settleConverterFor = (sCurrency?: string | null, sRate?: number | null) =>
-      sCurrency
-        ? tripConverter(sCurrency, sRate, tripCurrency, rates)
-        // The inverse of the display factor, so such a transfer reads back as entered.
-        : (amount: number) => amount / displayFactor;
+    const { currency, displayFactor, toDisplay, converterFor, settleConverterFor, isDirect } = settlementFx(opts);
     const unconvertedItems: number[] = [];
     const unconvertedSettlements: number[] = [];
     const unconvertedCurrencies = new Set<string>();
@@ -1158,7 +1097,7 @@ export class BudgetService {
     // and rounded to a cent once, at the boundary — from there on the ledger is
     // integer arithmetic, so Σ(balances) is exactly 0 and no sub-cent residual can
     // build up behind the two-decimal figures the user sees (#1382).
-    // `direct` is the half in display cents (#2965), see isDirect above.
+    // `direct` is the half in display cents (#2965), see isDirect in settlementFx.
     const balances: Record<
       number,
       { user_id: number; username: string; avatar_url: string | null; cents: number; direct: number }
diff --git a/server/tests/unit/nest/budget.service.db.test.ts b/server/tests/unit/nest/budget.service.db.test.ts
index ba32067e5..d8de90f8c 100644
--- a/server/tests/unit/nest/budget.service.db.test.ts
+++ b/server/tests/unit/nest/budget.service.db.test.ts
@@ -1807,20 +1807,14 @@ describe('the settlement converts with the quote the entry rate was frozen from
     const mine = before.finalBudgets.find(f => f.user_id === me.id)!;
     expect(mine.expenses).toBe(12345.67);
     expect(mine.sources.fronted).toEqual([{ item_id: bill.id, cents: 1234567 }]);
-    const offered = before.flows.map(f => f.amount);
-    expect(offered).toHaveLength(1);
-    expect([6172.83, 6172.84]).toContain(offered[0]);
-
-    // Bob pays exactly what settle-up offers, in dollars, as the Costs screen records it.
-    await budget.createSettlement(trip.id, { from_user_id: bob.id, to_user_id: me.id, amount: offered[0], currency: 'USD' }, me.id);
+    expect(before.flows.map(f => [6172.83, 6172.84].includes(f.amount))).toEqual([true]);
+    // Bob pays exactly what settle-up offers, in dollars; read in euros one cent may stay apart (#2965).
+    await budget.createSettlement(trip.id, { from_user_id: bob.id, to_user_id: me.id, amount: before.flows[0].amount, currency: 'USD' }, me.id);
     const after = await budget.settlement(trip.id, 'USD', 'EUR');
     expect(after.balances.map(b => b.balance)).toEqual([0, 0]);
     expect(after.flows).toEqual([]);
-    // Read in the trip currency both go through the euro, each rounded to a euro cent
-    // on its own, so at most that cent stays apart (#2965); it still adds up to zero.
-    const inEur = (await budget.settlement(trip.id, 'EUR', 'EUR')).balances.map(b => b.balance);
-    expect(inEur.every(b => Math.abs(b) <= 0.01)).toBe(true);
-    expect(Math.round(inEur[0] * 100) + Math.round(inEur[1] * 100)).toBe(0);
+    const inEur = (await budget.settlement(trip.id, 'EUR', 'EUR')).balances.map(b => Math.round(b.balance * 100));
+    expect([[0, 0], [1, -1], [-1, 1]]).toContainEqual(inEur);
   });
 
   it('BUDGET-SVC-DB-083: the final budget lists a bill at what was typed even where its trip cent rounds away', async () => {