diff --git a/chiron/analysis.py b/chiron/analysis.py
index 6550901..9608a81 100644
--- a/chiron/analysis.py
+++ b/chiron/analysis.py
@@ -4,6 +4,7 @@
 class MBAREstimator:
     def __init__(self, N_u: int) -> None:
         self.mbar_f_k = np.zeros(N_u)
+        self.mbar = None
 
     def initialize(self, u_kn: np.ndarray, N_k: np.ndarray):
         """
@@ -13,6 +14,18 @@ def initialize(self, u_kn: np.ndarray, N_k: np.ndarray):
         from loguru import logger as log
 
         log.debug(f"{N_k=}")
-        mbar = MBAR(u_kn=u_kn, N_k=N_k)
-        log.debug(mbar.f_k)
-        self.mbar_f_k = mbar.f_k
+        self.mbar = MBAR(u_kn=u_kn, N_k=N_k)
+
+    @property
+    def f_k(self):
+        from loguru import logger as log
+
+        log.debug(self.mbar.f_k)
+        return self.mbar.f_k
+
+    def get_free_energy_difference(self):
+        from loguru import logger as log
+
+        log.debug(self.mbar.f_k[-1])
+        self.f_k = self.mbar.f_k
+        return self.mbar_f_k[-1]
diff --git a/chiron/multistate.py b/chiron/multistate.py
index 713f1d0..6a0ba75 100644
--- a/chiron/multistate.py
+++ b/chiron/multistate.py
@@ -606,8 +606,25 @@ def _update_analysis(self):
         if self._offline_estimator:
             log.debug("Performing offline free energy estimate...")
             N_k = [self._iteration] * self.n_states
-            log.debug(f"{N_k=}")
             self._offline_estimator.initialize(
                 u_kn=self._energy_thermodynamic_states_for_each_iteration_in_run,
                 N_k=N_k,
             )
+        elif self._online_estimator:
+            log.debug("Performing online free energy estimate...")
+            self._online_estimator.update(
+                u_kn=self._energy_thermodynamic_states_for_each_iteration_in_run[
+                    :, :, self._iteration
+                ]
+            )
+        else:
+            raise RuntimeError("No free energy estimator provided.")
+
+    @property
+    def f_k(self):
+        if self._offline_estimator:
+            return self._offline_estimator.f_k
+        elif self._online_estimator:
+            return self._online_estimator.f_k
+        else:
+            raise RuntimeError("No free energy estimator found.")
diff --git a/chiron/tests/test_multistate.py b/chiron/tests/test_multistate.py
index ce74e1d..c316046 100644
--- a/chiron/tests/test_multistate.py
+++ b/chiron/tests/test_multistate.py
@@ -210,8 +210,6 @@ def test_multistate_run(ho_multistate_sampler_multiple_ks: MultiStateSampler):
     # check that the free energies are correct
     print(ho_sampler.analytical_f_i)
     print(ho_sampler.delta_f_ij_analytical)
-    print(ho_sampler._last_mbar_f_k_offline)
+    print(ho_sampler.f_k)
 
-    assert np.allclose(
-        ho_sampler.delta_f_ij_analytical[0], ho_sampler._last_mbar_f_k_offline, atol=0.1
-    )
+    assert np.allclose(ho_sampler.delta_f_ij_analytical[0], ho_sampler.f_k, atol=0.1)