OP, your mare will foal when she is good and ready to. Without the exact dates she was bred, you just can't predict a date. Vets can be wrong. And at this stage its difficult to tell how far along the foal is. And some mares carry longer. NewImages mare went over a year. ButtInTheDirts mare went what...13 months?
Unless she is in dire need of a vet, I wouldn't worry, sit back and relax until that foal is dropped. Then you can worry. Posted via Mobile Device