I believe you'll find KIA recommend it's 10000mls or 12 months from the previous service for petrol and 20000 or 12 months for diesel. So I believe you should have it done 12 months after the last service even it you haven't reached the mileage.. Ask a question to KCS and imagine they'll confirm that, but personally I'd keep to that to ensure there's no issues should you have a warranty claim.I have a 2017 Sportage GT-Line S purchased in September 2017. I did a higher mileage than normal in the first 30 months so in March 2020 as my mileage was just under 30000 miles I arranged my third service, a few days prior to lockdown (I did this without realising that the third service was not due until 36000 miles). Since then my mileage is still just a little less than 32000 miles and I have been approached by my local dealer to have the next service as it is almost 12 months since the last one. My question "as my service book states the fourth service interval is 4 years or 40000 miles whichever comes first, can I leave the service until September 2021 when the mileage will still be less than 40000 miles?"