diff --git a/tuttle/fx.py b/tuttle/fx.py
index e60208c6..c7154400 100644
--- a/tuttle/fx.py
+++ b/tuttle/fx.py
@@ -23,7 +23,7 @@
 from babel.numbers import get_territory_currencies
 
 from .app_db import AppDatabase
-from .tax import get_tax_system
+from .tax import NoTaxRules, tax_currency
 
 logger = logging.getLogger(__name__)
 
@@ -94,8 +94,8 @@ def default_currency(country: str) -> str:
     otherwise); else EUR.
     """
     try:
-        return get_tax_system(country).currency
-    except NotImplementedError:
+        return tax_currency(country)
+    except NoTaxRules:
         pass
     code = _COUNTRY_ALIASES.get(country)
     if code is None:
diff --git a/tuttle/tax.py b/tuttle/tax.py
index 802c4322..753ef564 100644
--- a/tuttle/tax.py
+++ b/tuttle/tax.py
@@ -5,7 +5,8 @@
 thresholds, polynomial coefficients, surcharge rates, VAT rates).
 
 The engine loads the right year's data for any given date, so historical
-invoices are taxed with the rules that were actually in force.
+invoices are taxed with the rules that were actually in force. A year
+without its own file has no tax rules: no other year's stand in for it.
 
 Adding a new year:  copy the JSON file, update the coefficients.
 Adding a new country: create a new subdirectory with its own JSON files.
@@ -103,19 +104,23 @@ def _resolve_country(country: str) -> str:
 def _get_params(country: str, year: int) -> TaxParams:
     """Get TaxParams for a country and year.
 
-    Falls back to the closest available year if the exact year isn't found.
+    A year without its own data raises ``NoTaxRules``: another year's rules
+    would pass for that year's, and the estimate with them.
     """
     canonical = _resolve_country(country)
-    years = _REGISTRY[canonical]
-    if year in years:
-        return years[year]
-    # Fall back: the most recent past year, else the earliest one we have
-    available = sorted(years.keys())
-    best = available[0]
-    for y in available:
-        if y <= year:
-            best = y
-    return years[best]
+    params = _REGISTRY[canonical].get(year)
+    if params is None:
+        raise NoTaxRules(f"No tax rules for {canonical} in {year}.")
+    return params
+
+
+def tax_currency(country: str) -> str:
+    """The currency *country*'s tax rules are written in, whatever the year.
+
+    Raises ``NoTaxRules`` when there is no tax model for *country*.
+    """
+    years = _REGISTRY[_resolve_country(country)]
+    return years[max(years)].currency
 
 
 def supported_countries() -> list[str]:
@@ -361,7 +366,7 @@ def get_tax_system(
               Defaults to today.
 
     Raises:
-        NoTaxRules: If the country has no data packages.
+        NoTaxRules: If the country has no data packages, or none for the year.
     """
     if date is None:
         date = datetime.date.today()
diff --git a/tuttle/tax_reserves.py b/tuttle/tax_reserves.py
index 7483e383..fd9d2549 100644
--- a/tuttle/tax_reserves.py
+++ b/tuttle/tax_reserves.py
@@ -12,7 +12,7 @@
 
 from pandas import DataFrame
 
-from .fx import convert, fx_haircut
+from .fx import convert, default_currency, fx_haircut
 from .fx import rate as fx_rate
 from .model import Invoice, Project, RecurringExpense
 from .tax import NoTaxRules, get_tax_system
@@ -235,8 +235,8 @@ def compute_income_tax_reserve(
     system's). The tariff is written in the tax system's currency, so income
     in another one is converted for it, and the tax back.
 
-    Raises ``NoTaxRules`` when there are no tax rules for *country*: a tax of
-    zero would pass for an estimate, so there is none.
+    Raises ``NoTaxRules`` when there are no tax rules for *country* in that
+    year: a tax of zero would pass for an estimate, so there is none.
     """
     today = datetime.date.today()
     _zero = IncomeTaxReserve(
@@ -324,9 +324,9 @@ def compute_spendable_income(
     year, as computed by ``forecasting.contracted_revenue``; other years
     ignore it.
 
-    Without tax rules for *country* the figures up to the tax base stay, and
-    the income tax, the expenses charged on taxed income and Safe to Spend
-    are None, with ``tax_unavailable_reason`` saying why.
+    Without tax rules for *country* in the year, the figures up to the tax
+    base stay, and the income tax, the expenses charged on taxed income and
+    Safe to Spend are None, with ``tax_unavailable_reason`` saying why.
     """
     today = datetime.date.today()
     # Any year but the current one is over: it has no planned or contracted work.
@@ -335,14 +335,7 @@ def compute_spendable_income(
     year_end = datetime.date(year or today.year, 12, 31)
     cent = Decimal("0.01")
 
-    ref_date = datetime.date(year, 7, 1) if year is not None else today
-
-    if currency is None:
-        try:
-            tax_system = get_tax_system(country, date=ref_date)
-            currency = tax_system.currency
-        except NotImplementedError:
-            pass
+    currency = currency or default_currency(country)
 
     received_gross = Decimal(0)
     received_vat = Decimal(0)
@@ -625,12 +618,7 @@ def compute_effective_salary(
     this_month = today.replace(day=1)
     cent = Decimal("0.01")
 
-    if currency is None:
-        try:
-            tax_system = get_tax_system(country, date=today)
-            currency = tax_system.currency
-        except NotImplementedError:
-            currency = "EUR"
+    currency = currency or default_currency(country)
 
     # A draft is not invoiced yet, so it is neither revenue nor where the history starts.
     invoices = [inv for inv in invoices if inv.is_issued and not inv.cancelled]
diff --git a/tuttle_tests/test_effective_salary.py b/tuttle_tests/test_effective_salary.py
index 7e654c8b..27927796 100644
--- a/tuttle_tests/test_effective_salary.py
+++ b/tuttle_tests/test_effective_salary.py
@@ -9,7 +9,7 @@
 
 import pytest
 
-from tuttle import tax_reserves
+from tuttle import tax, tax_reserves
 from tuttle.model import RecurringExpense
 from tuttle.tax_reserves import compute_effective_salary, compute_spendable_income
 from tuttle.time import Cycle
@@ -68,9 +68,12 @@ def test_steady_income_gives_the_same_salary_all_year(today, country):
     assert len(salaries) == 1
 
 
-def test_a_full_year_matches_safe_to_spend(today):
+def test_a_full_year_matches_safe_to_spend(today, monkeypatch):
     """On New Year's Day the salary averages exactly the year just closed."""
     today(datetime.date(2027, 1, 1))
+    # The salary is taxed with this year's rules, the estimate with 2026's: let
+    # 2027 have the same ones, so that only the averaging is compared.
+    monkeypatch.setitem(tax._REGISTRY["Germany"], 2027, tax.get_tax_system("Germany", datetime.date(2026, 7, 1)).params)
     invoices = _monthly_invoices(2026, range(1, 13))
     expenses = [_fixed("800"), _fixed("200", deductible=False)]
 
diff --git a/tuttle_tests/test_no_tax_estimate_without_year_data.py b/tuttle_tests/test_no_tax_estimate_without_year_data.py
new file mode 100644
index 00000000..a77bf4e7
--- /dev/null
+++ b/tuttle_tests/test_no_tax_estimate_without_year_data.py
@@ -0,0 +1,84 @@
+"""A year without its own tax rules gets no tax estimate: no other year's rules stand in."""
+
+import datetime
+from decimal import Decimal
+
+import pytest
+
+from tuttle import fx
+from tuttle.einvoice import _tax_currency
+from tuttle.model import Address, Client, Contract, Invoice, InvoiceItem, Project, User
+from tuttle.tax import NoTaxRules, available_years, get_tax_system, tax_currency
+from tuttle.tax_reserves import compute_income_tax_reserve, compute_spendable_income
+from tuttle.time import Cycle, TimeUnit
+
+FIRST = available_years("Germany")[0]
+LAST = available_years("Germany")[-1]
+
+
+def _invoice(date: datetime.date, net: str, currency: str = "EUR") -> Invoice:
+    client = Client(
+        name="Central Services",
+        address=Address(street="Main Street", number="42", postal_code="55555", city="Metro", country="Germany"),
+    )
+    contract = Contract(
+        title="Heating",
+        client=client,
+        rate=Decimal("100"),
+        currency=currency,
+        unit=TimeUnit.hour,
+        units_per_workday=8,
+        term_of_payment=14,
+        billing_cycle=Cycle.monthly,
+    )
+    project = Project(title="Boiler", tag="#boiler", start_date=date, contract=contract)
+    inv = Invoice(number=f"{date}-1", date=date, contract=contract, project=project, sent=True, paid=True)
+    InvoiceItem(invoice=inv, quantity=1, unit="flat", unit_price=Decimal(net), VAT_rate=Decimal("0"), description="Work")
+    return inv
+
+
+@pytest.mark.parametrize("year", [FIRST - 1, LAST + 1])
+def test_a_year_before_or_after_the_data_has_no_rules(year):
+    with pytest.raises(NoTaxRules, match=rf"^No tax rules for Germany in {year}\.$"):
+        get_tax_system("Germany", datetime.date(year, 7, 1))
+    with pytest.raises(NoTaxRules, match=rf"^No tax rules for Germany in {year}\.$"):
+        compute_income_tax_reserve(Decimal(50000), "Germany", year=year)
+
+
+def test_an_alias_is_named_by_its_country():
+    with pytest.raises(NoTaxRules, match=rf"^No tax rules for Germany in {LAST + 1}\.$"):
+        get_tax_system("Deutschland", datetime.date(LAST + 1, 7, 1))
+
+
+def test_a_year_with_data_is_unaffected():
+    assert get_tax_system("Germany", datetime.date(2025, 7, 1)).income_tax(Decimal(50000)) == 10691
+    assert compute_income_tax_reserve(Decimal(50000), "Germany", year=2025).ytd_reserve > 0
+
+
+@pytest.mark.parametrize("year", [FIRST - 1, LAST + 1])
+def test_tax_view_shows_no_estimate_for_that_year(year):
+    spending = compute_spendable_income([_invoice(datetime.date(year, 3, 1), "40000")], "Germany", currency="EUR", year=year)
+
+    assert spending.net_revenue_ytd == 40000
+    assert spending.tax_base == 40000
+    assert spending.income_tax_reserve is None
+    assert spending.spendable is None
+    assert spending.tax_unavailable_reason == f"No tax rules for Germany in {year}."
+
+
+def test_the_currency_does_not_depend_on_the_year():
+    assert tax_currency("United States") == "USD"
+    assert tax_currency("Deutschland") == "EUR"
+    with pytest.raises(NoTaxRules):
+        tax_currency("Norway")
+    assert fx.default_currency("United States") == "USD"
+    assert fx.default_currency("Norway") == "NOK"
+    assert _tax_currency(User(operating_country="United States")) == "USD"
+
+
+def test_without_a_currency_a_year_without_rules_still_converts():
+    """Foreign revenue is converted into the country's currency, not summed as it is."""
+    year = FIRST - 1
+    spending = compute_spendable_income([_invoice(datetime.date(year, 3, 1), "1000", currency="USD")], "Germany", year=year)
+    # USD 1,000 at the suite's stub rate of 0.9.
+    assert spending.net_revenue_ytd == 900
diff --git a/tuttle_tests/test_tax.py b/tuttle_tests/test_tax.py
index 9a6c38f1..91ea1bae 100644
--- a/tuttle_tests/test_tax.py
+++ b/tuttle_tests/test_tax.py
@@ -155,11 +155,10 @@ def _make_invoice(date, items_data, cancelled=False, vat_rate=None):
 
 
 class TestTaxSystemFramework:
-    def test_years_before_the_data_use_the_earliest_rules(self):
+    def test_years_before_the_data_have_no_rules(self):
         earliest = available_years("Germany")[0]
-        older = get_tax_system("Germany", date=datetime.date(earliest - 3, 6, 1))
-        first = get_tax_system("Germany", date=datetime.date(earliest, 6, 1))
-        assert older.income_tax(Decimal(50000)) == first.income_tax(Decimal(50000))
+        with pytest.raises(NoTaxRules, match=f"No tax rules for Germany in {earliest - 3}."):
+            get_tax_system("Germany", date=datetime.date(earliest - 3, 6, 1))
 
     def test_get_tax_system_germany(self):
         system = get_tax_system("Germany")
@@ -194,11 +193,10 @@ def test_year_selection(self):
         # Basic allowance increased 2024 → 2026
         assert sys_2024.params.basic_allowance < sys_2026.params.basic_allowance
 
-    def test_year_fallback(self):
-        """Year without data falls back to nearest available."""
-        sys = get_tax_system("Germany", date=datetime.date(2030, 1, 1))
-        # Should get the latest available year
-        assert sys.year == max(available_years("Germany"))
+    def test_years_after_the_data_have_no_rules(self):
+        """No other year's rules stand in for a year without its own."""
+        with pytest.raises(NoTaxRules, match="No tax rules for Germany in 2030."):
+            get_tax_system("Germany", date=datetime.date(2030, 1, 1))
 
 
 # ── German income tax ────────────────────────────────────────