If you’ve been waking up with an achy back or noticing a valley forming in the middle of your mattress, the problem might not actually be the mattress itself. Many homeowners assume a sagging bed means it’s time to buy an expensive new mattress, but often the real culprit is a tired bed frame or a worn-out box spring. Before you start shopping for a new bed, it’s worth taking a closer look at what’s underneath. This is a classic DIY home repair that a typical weekend warrior can tackle in a few hours with common tools and a little patience. And the best part? You can keep your current mattress and save some serious cash.

The first step is figuring out exactly what is sagging. Slide your mattress off the frame and take a good look at the foundation underneath. If you have a traditional box spring, check the wooden slats or the metal grid for cracks, broken wires, or missing support pieces. Box springs don’t last forever. After years of holding up a heavy mattress and two sleeping adults, the internal springs and wooden frame can give out. You might see a bowed wooden rail or a metal spring that has popped loose from its anchor. In that case, you don’t need to replace the whole bed. A few wood screws, a simple wooden brace, or replacing a single broken slat can bring flat support back.

If you have a platform bed with wooden slats, the remedy is often even simpler. Those slats are usually spaced several inches apart and held in place by the bed rail or a fabric strip. Over time, slats can crack, bend, or shift out of position, creating a weak spot that causes the mattress to dip. The fix is to remove the damaged slat, cut a new piece of plywood or solid lumber to the same length, and screw it into place. If your slats are simply bowing without breaking, you can add a center support beam. Most platform beds come with a single leg in the middle of the frame, but if that leg is missing or the bed is wider than a twin, adding a second leg can make a world of difference. A quick trip to the hardware store for a six-inch wooden post and a metal bracket will give you a sturdy middle support that takes the weight right off those tired slats.

Metal bed frames are another common source of sagging. These are the simple steel frames with a roller bar or a set of cross wires that hold the box spring. Over the years, the cross bars can bend, or the center support can buckle. The good news is that these frames are designed to be adjustable. You can often buy a replacement center support beam or a set of stronger cross slats that install without any tools. If the frame itself is bent, you might be able to straighten it with a rubber mallet and a block of wood, but if it’s severely warped, replacement is probably the safest route. A new metal bed frame is inexpensive and takes about twenty minutes to assemble.

One of the sneakiest causes of a sagging bed is something you might not think to check: the floor. If your bedroom floor is uneven, the bed frame might be twisting or rocking slightly, which makes the support system feel loose. Place a level on the floor next to the bed. If you find a dip, you can slide a thin shim under the bed legs to level the frame. This is a quick fix that removes stress from the frame and gives the mattress a flat, solid surface to rest on.

Another common DIY solution is to add a plywood sheet underneath the mattress. This works for nearly any type of bed frame. Measure the inside of your bed frame and buy a piece of quarter-inch or half-inch plywood cut to fit. Lay it directly on top of the slats or box spring, and then put your mattress back on top. The plywood bridges across any gaps or weak spots, giving you a continuous, flat surface. Just make sure not to use plywood that is too thick, or it might affect how the mattress breathes. A few small holes drilled into the plywood can help with airflow and prevent moisture buildup.

Whichever path you choose, reinforcing your bed foundation is a satisfying weekend project. It costs a fraction of what a new mattress would, and it often makes your current bed feel brand new. Your back will thank you, and you’ll get that solid, quiet, creak-free sleep you have been missing. So before you spend hundreds of dollars on a new mattress, try giving your bed frame a little DIY attention. It might be the simplest home repair you do all year.