Process for obtaining formic acid by thermal separation of a stream comprising formic acid and a tertiary amine (I), in which a liquid stream comprising formic acid and a tertiary amine (I) in a molar ratio of from 0.5 to 5 is produced by combining tertiary amine (I) and a formic acid source, from 10 to 100% by weight of the secondary components present therein are separated off and formic acid is removed by distillation in a distillation apparatus at a bottom temperature of from 100 to 300° C. and a pressure of from 30 to 3000 hPa abs from the liquid stream obtained, the bottom discharge from the distillation apparatus being separated into two liquid phases and the upper liquid phase being recycled to the formic acid source and the lower liquid phase being recycled for separating off the secondary components and/or to the distillation apparatus.