1st day of period 29/12; ovulation date 11/01 (28 day period). missed period 25/01 but slight pale spotting (once off). pregnancy test negative 27/01?

Home pregnancy tests are very accurate.: They are the same tests used in a doctors office. They can detect a pregnancy 7-10 days after conception. The best time to take one is when you miss your period.  if you doubt the result you can repeat it in 1-2 days. If you were pregnant the hormone level would rise enough for detection.

Unclear dates: The dates you provided are not quite clear, however, if you have missed your period and the pregnancy test was negative you may wish to repeat the test in 3-4 days, if you do not get your period. Use first morning urine and follow the instructions in the kit carefully.