Why did my equity decreased after the weekend (with fixed spread 12)

 

 Maybe this is a basic question but I can't figure this out

Why did my equity decreased more than usual from Friday 23:55  to Monday 00:00

Is there a commission I am being charged with? I am on Alpari demo server

2016.07.04 12:49:14.923 2015.01.05 00:05  macd EURUSD,M5: Bid1.192490 Ask1.192610 balance10000.63 L500 equity9848.030000 margin38.460400 freemargin9809.5696
2016.07.04 12:49:14.888 2015.01.05 00:00  macd EURUSD,M5: Bid1.194540 Ask1.194660 balance10000.63 L500 equity9880.830000 margin38.460400 freemargin9842.3696
2016.07.04 12:49:14.855 2015.01.02 23:55  macd EURUSD,M5: Bid1.200110 Ask1.200230 balance10000.63 L500 equity9971.230000 margin38.460400 freemargin9932.7696
2016.07.04 12:49:14.822 2015.01.02 23:50  macd EURUSD,M5: Bid1.200030 Ask1.200150 balance10000.63 L500 equity9969.950000 margin38.460400 freemargin9931.4896
...before

According to my C++ simulation the equity at 00:00 should have been 9882.11 instead of 9880.83

strategy tester is configured with a fixed spread of 12 pips on both

currently my formula for equity is balance + each order Bid-open price

...before
(test.cpp:65) equity+= -5.4 ( 1.20003 - 1.20543 )* 0.01 * 100000
(test.cpp:65) equity+= -4.26 ( 1.20003 - 1.20429 )* 0.01 * 100000
(test.cpp:65) equity+= -6.36 ( 1.20003 - 1.20321 )* 0.02 * 100000
(test.cpp:65) equity+= -8.43 ( 1.20003 - 1.20284 )* 0.03 * 100000
(test.cpp:65) equity+= -4.08 ( 1.20003 - 1.20105 )* 0.04 * 100000
(test.cpp:65) equity+= -2.15 ( 1.20003 - 1.20046 )* 0.05 * 100000
(test.cpp:69) total equity 9969.95
(strategy.h:68) 2015.01.02 23:50 Bid 1.20003 Ask 1.20015  balance 10000.63  equity 9969.95  margin 38.4604  freemargin 9931.4896
(test.cpp:65) equity+= -5.32 ( 1.20011 - 1.20543 )* 0.01 * 100000
(test.cpp:65) equity+= -4.18 ( 1.20011 - 1.20429 )* 0.01 * 100000
(test.cpp:65) equity+= -6.2 ( 1.20011 - 1.20321 )* 0.02 * 100000
(test.cpp:65) equity+= -8.19 ( 1.20011 - 1.20284 )* 0.03 * 100000
(test.cpp:65) equity+= -3.76 ( 1.20011 - 1.20105 )* 0.04 * 100000
(test.cpp:65) equity+= -1.75 ( 1.20011 - 1.20046 )* 0.05 * 100000
(test.cpp:69) total equity 9971.23
(strategy.h:68) 2015.01.02 23:55 Bid 1.20011 Ask 1.20023  balance 10000.63  equity 9971.23  margin 38.4604  freemargin 9932.7696
(test.cpp:65) equity+= -10.89 ( 1.19454 - 1.20543 )* 0.01 * 100000
(test.cpp:65) equity+= -9.75 ( 1.19454 - 1.20429 )* 0.01 * 100000
(test.cpp:65) equity+= -17.34 ( 1.19454 - 1.20321 )* 0.02 * 100000
(test.cpp:65) equity+= -24.9 ( 1.19454 - 1.20284 )* 0.03 * 100000
(test.cpp:65) equity+= -26.04 ( 1.19454 - 1.20105 )* 0.04 * 100000
(test.cpp:65) equity+= -29.6 ( 1.19454 - 1.20046 )* 0.05 * 100000
(test.cpp:69) total equity 9882.11
(strategy.h:68) 2015.01.05 00:00 Bid 1.19454 Ask 1.19466  balance 10000.63  equity 9882.11  margin 38.4604  freemargin 9843.6496
...equity is wrong from here
(test.cpp:65) equity+= -12.94 ( 1.19249 - 1.20543 )* 0.01 * 100000
(test.cpp:65) equity+= -11.8 ( 1.19249 - 1.20429 )* 0.01 * 100000
(test.cpp:65) equity+= -21.44 ( 1.19249 - 1.20321 )* 0.02 * 100000
(test.cpp:65) equity+= -31.05 ( 1.19249 - 1.20284 )* 0.03 * 100000
(test.cpp:65) equity+= -34.24 ( 1.19249 - 1.20105 )* 0.04 * 100000
(test.cpp:65) equity+= -39.85 ( 1.19249 - 1.20046 )* 0.05 * 100000
(test.cpp:69) total equity 9849.31
(strategy.h:68) 2015.01.05 00:05 Bid 1.19249 Ask 1.19261  balance 10000.63  equity 9849.31  margin 38.4604  freemargin 9810.8496
 

Besides prices that "gapped" down by at least 55 pips during the opening on Monday, you also have to consider the swap/roll-over costs: http://alpari.com/en/faq/trading_terms/overnight_swaps/

 
Alright thank you FMIC, I was not aware of that type of commissions, I have only seen that happen on weekends maybe it's different on real money accounts.
 
Orders held over 5 PM NY time have swap. Some brokers don't use the OrderCommission and OrderSwap but instead have entries in history (e.g. FXCM.)
Reason: