Originally Posted by Carbonfiberboy

Everyone needs to develop "base," especially if they are just starting to ride a lot. Developing base takes time. The adaptations come slowly. Think many months. So you commute now. Do you feel tired the next day when you commute? If so, slow down. Try to ride at a pace that doesn't leave you more tired the next day. So then after your week's commuting, you are also doing longer riders on the weekends. Manage your pace and distance on those rides so that again, the next day you don't feel significantly more tired or slower. But mostly manage your pace. Going hard for a short time isn't good for you now. Instead, go easy for a long time.

As has been suggested, keep track of your weekly mileage. Actually, keep track of your weekly time. If you always ride at about the same pace, the two may be interchangeable. However as you get stronger, you'll gradually ride faster, so time is really better. You can try increasing your weekly total time by 10% each week, though that may be too much, and like compound interest, it'll get away from you quite rapidly. So don't necessarily do that. Rather increase your weekly time at a rate that still allows you to recover between rides so that, as I said, you don't become progressively more tired from ride to ride. As you gradually build base in this fashion, your rides will naturally get longer. Don't rush the process. Feel your way along. It's good to reduce your volume about every 4th week, then resume at your former or a slightly increased volume. After 3 or 4 months of this process, you may want to reevaluate and try adding a little intensity by riding one or more of your rides at a faster pace, but carefully so that you don't need to take time off to recover.

Originally Posted by RR3

I don't know if this helps but I started cycling again 18 months ago. My first ride was 6 miles and it took me almost an hour (well 48 minutes to be precise IIRC). Adaptations take time. Building a base will increase the size and number of mitochondria as well as associated enzymes that allow you to ride longer distances without getting so tired. 25 miles now seems short to me. If your goal is to ride longer rides, slowly and consistently increase the distance of your one long ride per week. The one long ride per week is key in addition to riding at least four times per week. So, I went from fat and slow to contemplating trying to do over 420 miles in 24 hours next Winter and despite what another poster wrote, it ain't easy riding 22 mph nonstop. Again, the key is consistently increasing the load and particularly the long ride. 10-15% increases in mileage per week are the max. Every month or so, take an easy rest week (say maybe half the miles and lower intensity). Try to be patient. You can do it!