diff --git a/lib/models/credit.js b/lib/models/credit.js
index 69fd2a68..f93812cf 100644
--- a/lib/models/credit.js
+++ b/lib/models/credit.js
@@ -109,14 +109,16 @@ Credit.pre('validate', function(next) {
 
 // NB: Validate for docs that have promo amount
 Credit.pre('validate', function(next) {
-  if (this.promo_amount) {
-    // disallow coexistence of promo_amount and paid_amount/invoiced_amount
-    if (this.paid_amount || this.invoiced_amount) {
-      return next(new errors.BadRequestError(
-        'promo_amount cannot exist with invoiced_amount and/or paid_amount'
-      ));
-    }
+  // disallow coexistence of promo_amount and paid_amount/invoiced_amount
+  if (this.promo_amount !== null && this.promo_amount >= 0 &&
+    (this.paid_amount || this.invoiced_amount)) {
+    return next(new errors.BadRequestError(
+      'a positive or zero promo_amount cannot exist ' +
+      'with invoiced_amount and/or paid_amount'
+    ));
+  }
 
+  if (this.promo_amount !== null && this.promo_amount >= 0) {
     if (!this.promo_code) {
       return next(new errors.BadRequestError(
         'promo_amount must have valid promo_code'
@@ -130,6 +132,18 @@ Credit.pre('validate', function(next) {
     }
 
     return next();
+  } else {
+    if (this.promo_code) {
+      return next(new errors.BadRequestError(
+        'promo_code cannot exist with a negative promo_amount'
+      ));
+    }
+
+    if (this.promo_expires) {
+      return next(new errors.BadRequestError(
+        'promo_expires cannot exist with a negative promo_amount'
+      ));
+    }
   }
 
   next();
diff --git a/lib/models/payment-processor-adapters/stripe.js b/lib/models/payment-processor-adapters/stripe.js
index 32b6357d..43986f20 100644
--- a/lib/models/payment-processor-adapters/stripe.js
+++ b/lib/models/payment-processor-adapters/stripe.js
@@ -237,7 +237,7 @@ const stripeAdapter = {
     }
   },
 
-  balanceDebits: function(customerId, debits) {
+  balanceDebits: function(customerId, periodDebitTotal) {
     // -- get invoices
     // -- do "stripe balance" calcualation
     // -- check for min amount
@@ -254,11 +254,7 @@ const stripeAdapter = {
         console.log('got invoices...');
         console.log('invoiceTotal: %j', invoiceTotal);
 
-        const debitTotal = (debits
-          .reduce((result, debit) => result + debit.amount, 0.0) + 0.0);
-        console.log('debitTotal: %j', debitTotal);
-
-        const stripeBalance = debitTotal - invoiceTotal;
+        const stripeBalance = periodDebitTotal - invoiceTotal;
         console.log('stripeBalance: %j', stripeBalance);
 
         return new Promise((resolve, reject) => {
diff --git a/test/credit.unit.js b/test/credit.unit.js
index e1bcf010..178c3b8d 100644
--- a/test/credit.unit.js
+++ b/test/credit.unit.js
@@ -140,7 +140,7 @@ describe('Storage/models/Credit', function() {
 
   describe('#create - paid_amount and invoiced_amount relations', function() {
 
-    it('should fail if trying to save paid without invoiced', function(done) {
+    it('should fail if trying to save paid without invoiced_amount', function(done) {
       const newCredit = new Credit({
         user: 'user@domain.tld',
         type: CREDIT_TYPES.MANUAL,
@@ -173,7 +173,7 @@ describe('Storage/models/Credit', function() {
       });
     });
 
-    it('should set paid=true if paid=invoiced && both > 0', function(done) {
+    it('should set paid=true if paid_amount=invoiced_amount && both > 0', function(done) {
       const newCredit = new Credit({
         user: 'user@domain.tld',
         type: CREDIT_TYPES.MANUAL,
@@ -191,7 +191,7 @@ describe('Storage/models/Credit', function() {
       });
     });
 
-    it('should set paid=false if paid!=invoiced && both > 0', function(done) {
+    it('should set paid=false if paid_amount!=invoiced_amount && both > 0', function(done) {
       const newCredit = new Credit({
         user: 'user@domain.tld',
         type: CREDIT_TYPES.MANUAL,
@@ -247,9 +247,9 @@ describe('Storage/models/Credit', function() {
 
   });
 
-  describe('#create - promo vs paid_amount/invoiced_amount', function() {
+  describe('#create - promo_amount vs paid_amount/invoiced_amount', function() {
 
-    it('should fail if trying to save invoiced and promo', function(done) {
+    it('should fail if trying to save invoiced_amount and promo_amount', function(done) {
       const newCredit = new Credit({
         user: 'user@domain.tld',
         type: CREDIT_TYPES.MANUAL,
@@ -260,13 +260,13 @@ describe('Storage/models/Credit', function() {
       newCredit.save(function(err) {
         expect(err).to.be.an.instanceOf(Error);
         expect(err.message).to.equal(
-          'promo_amount cannot exist with invoiced_amount and/or paid_amount'
+          'a positive or zero promo_amount cannot exist with invoiced_amount and/or paid_amount'
         );
         done();
       });
     });
 
-    it('should fail if trying to save paid_amount and promo', function(done) {
+    it('should fail if trying to save paid_amount and promo_amount', function(done) {
       const newCredit = new Credit({
         user: 'user@domain.tld',
         type: CREDIT_TYPES.MANUAL,
@@ -277,13 +277,13 @@ describe('Storage/models/Credit', function() {
       newCredit.save(function(err) {
         expect(err).to.be.an.instanceOf(Error);
         expect(err.message).to.equal(
-          'promo_amount cannot exist with invoiced_amount and/or paid_amount'
+          'a positive or zero promo_amount cannot exist with invoiced_amount and/or paid_amount'
         );
         done();
       });
     });
 
-    it('should have no paid/invoice if promo exists', function(done) {
+    it('should have no paid_amount/invoiced_amount if promo_amount exists', function(done) {
       const newCredit = new Credit({
         user: 'user@domain.tld',
         type: CREDIT_TYPES.MANUAL,
@@ -308,7 +308,7 @@ describe('Storage/models/Credit', function() {
       });
     });
 
-    it('should have no promo if paid/invoice exists', function(done) {
+    it('should have no promo if paid_amount/invoiced_amount exists', function(done) {
       const newCredit = new Credit({
         user: 'user@domain.tld',
         type: CREDIT_TYPES.MANUAL,
@@ -329,7 +329,7 @@ describe('Storage/models/Credit', function() {
 
   });
 
-  describe('#create - promo validations', function() {
+  describe('#create - promo_amount validations', function() {
 
     it('should have promo_code if promo_amount is > 0', function(done) {
       const newCredit = new Credit({
@@ -350,6 +350,23 @@ describe('Storage/models/Credit', function() {
       });
     });
 
+    it('should fail if promo_amount is negative and there is a promo_expires', function(done) {
+      const newCredit = new Credit({
+        user: 'user@domain.tld',
+        type: CREDIT_TYPES.MANUAL,
+        promo_amount: -1,
+        promo_expires: PROMO_EXPIRES.NEW_SIGNUP
+      });
+
+      newCredit.save(function(err) {
+        expect(err).to.be.instanceOf(Error);
+        expect(err.message).to.equal(
+          'promo_expires cannot exist with a negative promo_amount'
+        );
+        done();
+      });
+    });
+
     it('should fail if promo_amount > 0 && !promo_code', function(done) {
       const newCredit = new Credit({
         user: 'user@domain.tld',
@@ -377,7 +394,7 @@ describe('Storage/models/Credit', function() {
 
       newCredit.save(function(err) {
         expect(err).to.be.an.instanceOf(Error);
-        expect(err.message).to.equal('Credit validation failed');
+        expect(err.message).to.equal('promo_code cannot exist with a negative promo_amount');
         done();
       });
     });
@@ -515,7 +532,7 @@ describe('Storage/models/Credit', function() {
       });
     });
 
-    it('should have specified fields for promo', function(done) {
+    it('should have specified fields for creating promo', function(done) {
       const newCredit = new Credit({
         user: 'user@domain.tld',
         type: CREDIT_TYPES.MANUAL,