diff --git a/hgvsparser/to_model.py b/hgvsparser/to_model.py
index e243d36..e0f0564 100644
--- a/hgvsparser/to_model.py
+++ b/hgvsparser/to_model.py
@@ -114,7 +114,7 @@ def add_token(parent, token_type, token_value):
     if isinstance(parent, dict):
         if token_type == 'POSITION':
             if token_value != '?':
-                parent['position'] = int(token_value) - 1
+                parent['position'] = int(token_value)
             else:
                 parent['uncertain'] = True
         elif token_type == 'OFFSET':

0 vs 1 offsets
I was surprised to find my locations shift -1.
A parser shouldnt make any semantic changes probably.
diff --git a/tests/test_convert.py b/tests/test_convert.py
index 3daec68..e149ce2 100644
--- a/tests/test_convert.py
+++ b/tests/test_convert.py
@@ -360,7 +360,7 @@ def test_reference_part(description, model):
 VARIANTS = [
     # Substitutions
     (
-        '101C>A',
+        '100C>A',
         {
             'variants': [
                 {
@@ -387,7 +387,7 @@ VARIANTS = [
         }
     ),
     (
-        '101+3C>A',
+        '100+3C>A',
         {
             'variants': [
                 {
@@ -417,7 +417,7 @@ VARIANTS = [
         }
     ),
     (
-        '*101C>A',
+        '*100C>A',
         {
             'variants': [
                 {
@@ -453,7 +453,7 @@ VARIANTS = [
                     'source': 'reference',
                     'location': {
                         'type': 'point',
-                        'position': 0,
+                        'position': 1,
                         'offset': {
                             'value': -3,
                         },
@@ -484,7 +484,7 @@ VARIANTS = [
                     'source': 'reference',
                     'location': {
                         'type': 'point',
-                        'position': 0,
+                        'position': 1,
                         'offset': {
                             'value': 3,
                         },
@@ -508,7 +508,7 @@ VARIANTS = [
     ),
     # Deletions
     (
-        '11del',
+        '10del',
         {
             'variants': [
                 {
@@ -524,7 +524,7 @@ VARIANTS = [
     ),
     (
         # Note: the addition of 'A' is not HGVS.
-        '11delA',
+        '10delA',
         {
             'variants': [
                 {
@@ -545,7 +545,7 @@ VARIANTS = [
         }
     ),
     (
-        '101+1del',
+        '100+1del',
         {
             'variants': [
                 {
@@ -563,7 +563,7 @@ VARIANTS = [
         }
     ),
     (
-        '11_21del',
+        '10_20del',
         {
             'variants': [
                 {
@@ -585,7 +585,7 @@ VARIANTS = [
         }
     ),
     (
-        '11-1_21-3del',
+        '10-1_20-3del',
         {
             'variants': [
                 {
@@ -614,7 +614,7 @@ VARIANTS = [
     ),
     (
         # Note: the addition of '5' is not HGVS.
-        '11_16del5',
+        '10_15del5',
         {
             'variants': [
                 {
@@ -642,7 +642,7 @@ VARIANTS = [
         }
     ),
     (
-        '(11_16)del',
+        '(10_15)del',
         {
             'variants': [
                 {
@@ -665,7 +665,7 @@ VARIANTS = [
         }
     ),
     (
-        '(11_21)_31del',
+        '(10_20)_30del',
         {
             'variants': [
                 {
@@ -695,7 +695,7 @@ VARIANTS = [
         }
     ),
     (
-        '(11_21)_(31_41)del',
+        '(10_20)_(30_40)del',
         {
             'variants': [
                 {
@@ -733,7 +733,7 @@ VARIANTS = [
         }
     ),
     (
-        '(?_-21)_(31+1_31-1)del',
+        '(?_-20)_(30+1_30-1)del',
         {
             'variants': [
                 {
@@ -795,7 +795,7 @@ VARIANTS = [
                             },
                             'end': {
                                 'type': 'point',
-                                'position': 0,
+                                'position': 1,
                                 'outside_cds': 'upstream'
                             }
                         },
@@ -804,7 +804,7 @@ VARIANTS = [
                             'uncertain': True,
                             'start': {
                                 'type': 'point',
-                                'position': 0,
+                                'position': 1,
                                 'outside_cds': 'downstream'
                             },
                             'end': {
@@ -835,7 +835,7 @@ VARIANTS = [
                             },
                             'end': {
                                 'type': 'point',
-                                'position': 0,
+                                'position': 1,
                                 'outside_cds': 'upstream',
                                 'offset': {
                                     'uncertain': True
@@ -847,7 +847,7 @@ VARIANTS = [
                             'uncertain': True,
                             'start': {
                                 'type': 'point',
-                                'position': 0,
+                                'position': 1,
                                 'outside_cds': 'downstream',
                                 'offset':  {
                                     'uncertain': True
@@ -865,7 +865,7 @@ VARIANTS = [
     ),
     # Duplications
     (
-        '11dup',
+        '10dup',
         {
             'variants': [
                 {
@@ -884,7 +884,7 @@ VARIANTS = [
     #    variant level (and not only in the 'inserted') is that an 'insertion'
     #    is considered a special case of a 'deletion_insertion'.
     (
-        '11_12insT',
+        '10_11insT',
         {
             'variants': [
                 {
@@ -912,7 +912,7 @@ VARIANTS = [
         }
     ),
     (
-        '11_12ins[T]',
+        '10_11ins[T]',
         {
             'variants': [
                 {
@@ -940,7 +940,7 @@ VARIANTS = [
         }
     ),
     (
-        '11_12ins[T;11_21]',
+        '10_11ins[T;10_20]',
         {
             'variants': [
                 {
@@ -981,7 +981,7 @@ VARIANTS = [
         }
     ),
     (
-        '11_12ins[T;11_21inv]',
+        '10_11ins[T;10_20inv]',
         {
             'variants': [
                 {
@@ -1024,7 +1024,7 @@ VARIANTS = [
         }
     ),
     (
-        '11_12ins[T;11_21inv;NM_000001.1:c.101_201]',
+        '10_11ins[T;10_20inv;NM_000001.1:c.100_200]',
         {
             'references': {
                 'NM_000001.1': {
@@ -1088,7 +1088,7 @@ VARIANTS = [
         }
     ),
     (
-        '11_12insNM_000001.1:c.101_201',
+        '10_11insNM_000001.1:c.100_200',
         {
             'references': {
                 'NM_000001.1': {
@@ -1133,7 +1133,7 @@ VARIANTS = [
         }
     ),
     (
-        '11_12insNM_000001.1',
+        '10_11insNM_000001.1',
         {
             'references': {
                 'NM_000001.1': {
@@ -1167,7 +1167,7 @@ VARIANTS = [
         }
     ),
     (
-        '11_12insNG_000001.1(NM_000002.3):c.100',
+        '10_11insNG_000001.1(NM_000002.3):c.100',
         {
             'references': {
                 'NG_000001.1': {
@@ -1196,7 +1196,7 @@ VARIANTS = [
                             'source': 'NG_000001.1(NM_000002.3):c.',
                             'location': {
                                 'type': 'point',
-                                'position': 99
+                                'position': 100
                             },
                         }
                     ]
@@ -1206,7 +1206,7 @@ VARIANTS = [
     ),
     # Inversions
     (
-        '11_12inv',
+        '10_11inv',
         {
             'variants': [
                 {
@@ -1229,7 +1229,7 @@ VARIANTS = [
     ),
     # Conversions
     (
-        '11_21con31_41',
+        '10_20con30_40',
         {
             'variants': [
                 {
@@ -1268,7 +1268,7 @@ VARIANTS = [
     ),
     # Deletion-inserted
     (
-        '11delinsGA',
+        '10delinsGA',
         {
             'variants': [
                 {
@@ -1289,7 +1289,7 @@ VARIANTS = [
         }
     ),
     (
-        '11_21delinsGA',
+        '10_20delinsGA',
         {
             'variants': [
                 {
@@ -1327,11 +1327,11 @@ VARIANTS = [
                         'type': 'range',
                         'start': {
                             'type': 'point',
-                            'position': 10
+                            'position': 11
                         },
                         'end': {
                             'type': 'point',
-                            'position': 20
+                            'position': 21
                         }
                     },
                     'deleted': [
@@ -1359,7 +1359,7 @@ VARIANTS = [
                     'source': 'reference',
                     'location': {
                         'type': 'point',
-                        'position': 10
+                        'position': 11
                     },
                     'deleted': [
                         {
@@ -1441,7 +1441,7 @@ VARIANTS = [
         }
     ),
     (
-        '11=',
+        '10=',
         {
             'variants': [
                 {
@@ -1456,7 +1456,7 @@ VARIANTS = [
         }
     ),
     (
-        '11_21=',
+        '10_20=',
         {
             'variants': [
                 {
@@ -1479,7 +1479,7 @@ VARIANTS = [
     ),
     # Multiple variants (allele)
     (
-        '[11=;11_12ins[T;11_21inv;NM_000001.1:c.101_201];11_21delinsGA]',
+        '[10=;10_11ins[T;10_20inv;NM_000001.1:c.100_200];10_20delinsGA]',
         {
             'references': {
                 'NM_000001.1': {

pip install -e .[dev]
parse_log_pytest
requirements.txt
pytest pytest-cov pytest-xdist pytest-mock pytest-asyncio pytest-bdd pytest-benchmark pytest-randomly responses mock hypothesis freezegun trustme requests-mock requests tomlkit
apt-get update apt-get install -y gcc
3.9
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
attrs==25.3.0
certifi==2025.1.31
cffi==1.17.1
charset-normalizer==3.4.1
coverage==7.8.0
cryptography==44.0.2
exceptiongroup==1.2.2
execnet==2.1.1
freezegun==1.5.1
gherkin-official==29.0.0
-e git+https://github.com/mutalyzer/hgvs-parser.git@035ca562875b4e9b2402147a1260686d7c676407#egg=hgvsparser
hypothesis==6.130.5
idna==3.10
importlib_metadata==8.6.1
iniconfig==2.1.0
lark-parser==0.6.4
Mako==1.3.9
MarkupSafe==3.0.2
mock==5.2.0
packaging==24.2
parse==1.20.2
parse_type==0.6.4
pluggy==1.5.0
py==1.5.2
py-cpuinfo==9.0.0
pycparser==2.22
pydot==1.2.4
pyparsing==2.2.0
pytest==8.3.5
pytest-asyncio==0.26.0
pytest-bdd==8.1.0
pytest-benchmark==5.1.0
pytest-cov==6.0.0
pytest-mock==3.14.0
pytest-randomly==3.16.0
pytest-xdist==3.6.1
python-dateutil==2.9.0.post0
PyYAML==6.0.2
requests==2.32.3
requests-mock==1.12.1
responses==0.25.7
six==1.17.0
sortedcontainers==2.4.0
tomli==2.2.1
tomlkit==0.13.2
trustme==1.2.1
typing_extensions==4.13.0
urllib3==2.3.0
zipp==3.21.0

name: hgvs-parser
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.4.4=h6a678d5_1
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=3.0.16=h5eee18b_0
  - pip=25.0=py39h06a4308_0
  - python=3.9.21=he870216_1
  - readline=8.2=h5eee18b_0
  - setuptools=75.8.0=py39h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - tzdata=2025a=h04d1e81_0
  - wheel=0.45.1=py39h06a4308_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - attrs==25.3.0
      - certifi==2025.1.31
      - cffi==1.17.1
      - charset-normalizer==3.4.1
      - coverage==7.8.0
      - cryptography==44.0.2
      - exceptiongroup==1.2.2
      - execnet==2.1.1
      - freezegun==1.5.1
      - gherkin-official==29.0.0
      - hypothesis==6.130.5
      - idna==3.10
      - importlib-metadata==8.6.1
      - iniconfig==2.1.0
      - lark-parser==0.6.4
      - mako==1.3.9
      - markupsafe==3.0.2
      - mock==5.2.0
      - packaging==24.2
      - parse==1.20.2
      - parse-type==0.6.4
      - pluggy==1.5.0
      - py==1.5.2
      - py-cpuinfo==9.0.0
      - pycparser==2.22
      - pydot==1.2.4
      - pyparsing==2.2.0
      - pytest==8.3.5
      - pytest-asyncio==0.26.0
      - pytest-bdd==8.1.0
      - pytest-benchmark==5.1.0
      - pytest-cov==6.0.0
      - pytest-mock==3.14.0
      - pytest-randomly==3.16.0
      - pytest-xdist==3.6.1
      - python-dateutil==2.9.0.post0
      - pyyaml==6.0.2
      - requests==2.32.3
      - requests-mock==1.12.1
      - responses==0.25.7
      - six==1.17.0
      - sortedcontainers==2.4.0
      - tomli==2.2.1
      - tomlkit==0.13.2
      - trustme==1.2.1
      - typing-extensions==4.13.0
      - urllib3==2.3.0
      - zipp==3.21.0
prefix: /opt/conda/envs/hgvs-parser

tests/test_convert.py::test_variants[100+3C>A-model1] tests/test_convert.py::test_variants[10_20delinsGA-model29] tests/test_convert.py::test_variants[10_15del5-model10] tests/test_convert.py::test_variants[10_11insT-model18] tests/test_convert.py::test_variants[10_11insNM_000001.1-model24] tests/test_convert.py::test_variants[100C>A-model0] tests/test_convert.py::test_variants[11delAinsGA-model31] tests/test_convert.py::test_variants[-1+3C>A-model4] tests/test_convert.py::test_variants[(10_20)_(30_40)del-model13] tests/test_convert.py::test_variants[[10=;10_11ins[T;10_20inv;NM_000001.1:c.100_200];10_20delinsGA]-model35] tests/test_convert.py::test_variants[*100C>A-model2] tests/test_convert.py::test_variants[10_20=-model34] tests/test_convert.py::test_variants[(10_15)del-model11] tests/test_convert.py::test_variants[100+1del-model7] tests/test_convert.py::test_variants[10delA-model6] tests/test_convert.py::test_variants[10=-model33] tests/test_convert.py::test_variants[10_11ins[T;10_20inv]-model21] tests/test_convert.py::test_variants[10_11insNM_000001.1:c.100_200-model23] tests/test_convert.py::test_variants[(10_20)_30del-model12] tests/test_convert.py::test_variants[10dup-model17] tests/test_convert.py::test_variants[11_21del10insGA-model30] tests/test_convert.py::test_variants[10_11inv-model26] tests/test_convert.py::test_variants[10del-model5] tests/test_convert.py::test_variants[10-1_20-3del-model9] tests/test_convert.py::test_variants[10_11insNG_000001.1(NM_000002.3):c.100-model25] tests/test_convert.py::test_variants[10_11ins[T]-model19] tests/test_convert.py::test_variants[10_11ins[T;10_20inv;NM_000001.1:c.100_200]-model22] tests/test_convert.py::test_variants[10_20del-model8] tests/test_convert.py::test_variants[10_11ins[T;10_20]-model20] tests/test_convert.py::test_variants[(?_-1)_(*1_?)del-model15] tests/test_convert.py::test_variants[10_20con30_40-model27] tests/test_convert.py::test_variants[10delinsGA-model28] tests/test_convert.py::test_variants[*1-3C>A-model3] tests/test_convert.py::test_variants[(?_-20)_(30+1_30-1)del-model14] tests/test_convert.py::test_variants[(?_-1+?)_(*1-?_?)del-model16]
tests/test_convert.py::test_reference_part[LRG_24p1-model18] tests/test_convert.py::test_reference_part[NG_012337.1(TIMM8B_v001)-model11] tests/test_convert.py::test_reference_part[NG_012337.1(TIMM8B_i001)-model12] tests/test_convert.py::test_reference_part[NC_012920.1(MT-TL1)-model7] tests/test_convert.py::test_reference_part[NC_000001(SDHD_v001)-model9] tests/test_convert.py::test_reference_part[NC_000001.1p1-model20] tests/test_convert.py::test_reference_part[NC_012920.1(MT-TL1_i001):c.-model15] tests/test_convert.py::test_reference_part[LRG_24(SDHD):c.-model22] tests/test_convert.py::test_reference_part[LRG_1-model3] tests/test_convert.py::test_reference_part[NC_000001-model0] tests/test_convert.py::test_reference_part[NC_000001.1t1-model19] tests/test_convert.py::test_variants[=-model32] tests/test_convert.py::test_reference_part[NC_000001(SDHD)-model6] tests/test_convert.py::test_reference_part[NC_000001.10:c.-model2] tests/test_convert.py::test_reference_part[LRG_1.1-model5] tests/test_convert.py::test_reference_part[NC_012920.1(MT-TL1_i001)-model14] tests/test_convert.py::test_reference_part[LRG_24t1-model17] tests/test_convert.py::test_reference_part[NC_000001.10-model1] tests/test_convert.py::test_reference_part[NG_012337.1(NM_012459.2)-model16] tests/test_convert.py::test_reference_part[NC_012920.1(MT-TL1_v001)-model13] tests/test_convert.py::test_reference_part[LRG_1:g.-model4] tests/test_convert.py::test_reference_part[NG_012337.1(TIMM8B)-model8] tests/test_convert.py::test_reference_part[LRG_24(SDHD)-model21] tests/test_convert.py::test_reference_part[NC_000001(SDHD_i001)-model10]
hgvsparser/to_model.py
hgvsparser/to_model.py