The impact of a remap on fuel consumption depends entirely on how you drive. This might sound evasive, but it's genuinely true — and here's why.
A quality Stage 1 calibration optimises combustion efficiency. At partial throttle (normal driving), the engine can actually operate more efficiently than stock because the calibration improves torque delivery at lower RPMs, meaning you need less throttle to maintain the same speed.
However, if you use the additional performance frequently — more aggressive acceleration, higher sustained speeds — consumption will increase. The engine is producing more power, and power requires fuel.
Real-world experience: most owners who drive normally report no significant change in fuel consumption, and some diesel owners report a slight improvement on long motorway runs. Owners who enjoy the additional performance typically see 5-15% increased consumption.