diff --git a/.gitignore b/.gitignore
index b9d6bd9..e0cdfde 100644
--- a/.gitignore
+++ b/.gitignore
@@ -213,3 +213,4 @@ pip-log.txt
 
 #Mr Developer
 .mr.developer.cfg
+.Rproj.user
diff --git a/DESCRIPTION b/DESCRIPTION
index 12a52bc..ca6a943 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,8 +1,8 @@
 Package: FinCal
 Title: Time Value of Money, Time Series Analysis and Computational Finance
 Description: Package for time value of money calculation, time series analysis and computational finance.
-Version: 0.6.4
-Date: 2017-04-12
+Version: 0.6.5
+Date: 2023-08-05
 Author: Felix Yanhui Fan <nolanfyh@gmail.com>
 Imports:
     ggplot2,
diff --git a/R/fv.annuity.R b/R/fv.annuity.R
index dec8fa7..f8080bb 100644
--- a/R/fv.annuity.R
+++ b/R/fv.annuity.R
@@ -14,8 +14,12 @@ fv.annuity <- function(r,n,pmt,type=0) {
   if(type != 0 && type !=1){
     print("Error: type should be 0 or 1!")
   }else{
-  fv = (pmt / r * ((1 + r)^n - 1))*(1+r)^type * (-1)
-  return(fv)
+    fv = if (isTRUE(all.equal(0.0, r))){
+      pmt * n * (-1)
+    }else{
+      (pmt / r * ((1 + r)^n - 1))*(1+r)^type * (-1)
+    }
+    return(fv)
   }
 }
 
diff --git a/R/n.period.R b/R/n.period.R
index 9dc9fea..badd7e4 100644
--- a/R/n.period.R
+++ b/R/n.period.R
@@ -18,8 +18,12 @@ n.period <- function(r,pv,fv,pmt,type=0){
   if(type != 0 && type !=1){
     print("Error: type should be 0 or 1!")
   }else{
-  n <- log(-1 * (fv*r-pmt* (1+r)^type)/(pv*r+pmt* (1+r)^type))/log(1+r)
-  return(n)
+    n <-  if (isTRUE(all.equal(0.0, r))){
+      -1 * (fv+pv) / pmt
+    }else{
+      log(-1 * (fv*r-pmt* (1+r)^type)/(pv*r+pmt* (1+r)^type))/log(1+r)
+    }
+    return(n)
   }
 }
 
diff --git a/R/pmt.R b/R/pmt.R
index 68a04dd..5a789f7 100644
--- a/R/pmt.R
+++ b/R/pmt.R
@@ -19,7 +19,11 @@ pmt <- function(r,n,pv,fv,type=0){
   if(type != 0 && type !=1){
     print("Error: type should be 0 or 1!")
   }else{
-  pmt <- (pv+fv/(1+r)^n)*r/(1-1/(1+r)^n) * (-1) * (1+r)^(-1 * type)
+  pmt <-  if (isTRUE(all.equal(0.0, r))){
+    (pv+fv)/n * (-1)
+  }else{
+    (pv+fv/(1+r)^n)*r/(1-1/(1+r)^n) * (-1) * (1+r)^(-1 * type)
+  }
   return(pmt)
   }
 }
diff --git a/R/pv.annuity.R b/R/pv.annuity.R
index c030e7a..080f39b 100644
--- a/R/pv.annuity.R
+++ b/R/pv.annuity.R
@@ -14,7 +14,11 @@ pv.annuity <- function(r, n, pmt, type=0) {
   if(type != 0 && type !=1){
     print("Error: type should be 0 or 1!")
   }else{
-  pv = (pmt / r * (1 - 1 / (1 + r)^n))*(1 + r)^type * (-1)
-  return(pv)
+    pv = if (isTRUE(all.equal(0.0, r))){
+      n * pmt * (-1)
+    }else{
+      (pmt / r * (1 - 1 / (1 + r)^n))*(1 + r)^type * (-1)
+    }
+    return(pv)
   }
 }